diff --git a/data/simulation/config.d.ts b/data/simulation/config.d.ts
index 02b0b648a..e52572244 100644
--- a/data/simulation/config.d.ts
+++ b/data/simulation/config.d.ts
@@ -39,10 +39,10 @@ export interface Config {
    * Only supported by Haskell simulation. */
   "leios-vote-send-recv-stages": boolean;
   /**
-   * Extends Leios so that EB producers include IBs directly from previous pipelines
-   * where no certified EB was observed.
-   * 
-   * Only supported by Rust simulation. */
+   * Extends Leios so that EB producers include IBs directly from previous pipelines.
+   * Due to casuality, the EB must always include them, even if those IBs end up being
+   * certified in their own pipeline.
+   */
   "leios-late-ib-inclusion": boolean;
   /**
    * The expected time it takes a header to fully diffuse across the network.
diff --git a/data/simulation/variants/config.full.yaml b/data/simulation/variants/config.full.yaml
index 98bd69dba..fc73ec405 100644
--- a/data/simulation/variants/config.full.yaml
+++ b/data/simulation/variants/config.full.yaml
@@ -4,7 +4,7 @@ leios-variant: full
 # "Random" is meant to ensure that different producers include different TXs.
 leios-mempool-sampling-strategy: random
 
-# Allow EBs to include IBs from previous slots
+# Allow EBs to include IBs from previous pipelines
 leios-late-ib-inclusion: true
 
 # Chain quality controls how far back EB recursion can reach.
diff --git a/leios-trace-hs/src/LeiosConfig.hs b/leios-trace-hs/src/LeiosConfig.hs
index 6ff097025..c0a2902e1 100644
--- a/leios-trace-hs/src/LeiosConfig.hs
+++ b/leios-trace-hs/src/LeiosConfig.hs
@@ -99,6 +99,7 @@ data Config = Config
   , leiosStageActiveVotingSlots :: Word
   , leiosVoteSendRecvStages :: Bool
   , leiosVariant :: LeiosVariant
+  , leiosLateIbInclusion :: Bool
   , leiosHeaderDiffusionTimeMs :: DurationMs
   , praosChainQuality :: Double
   , txGenerationDistribution :: Distribution
@@ -171,6 +172,7 @@ instance Default Config where
       , leiosStageActiveVotingSlots = 1
       , leiosVoteSendRecvStages = False
       , leiosVariant = Short
+      , leiosLateIbInclusion = True
       , leiosHeaderDiffusionTimeMs = 1000
       , praosChainQuality = 40
       , txGenerationDistribution = Exp{lambda = 0.85, scale = Just 1000}
@@ -243,6 +245,7 @@ configToKVsWith getter cfg =
     , get @"treatBlocksAsFull" getter cfg
     , get @"cleanupPolicies" getter cfg
     , get @"leiosVariant" getter cfg
+    , get @"leiosLateIbInclusion" getter cfg
     , get @"leiosHeaderDiffusionTimeMs" getter cfg
     , get @"praosChainQuality" getter cfg
     , get @"simulateTransactions" getter cfg
@@ -329,6 +332,7 @@ instance FromJSON Config where
     treatBlocksAsFull <- parseFieldOrDefault @Config @"treatBlocksAsFull" obj
     cleanupPolicies <- parseFieldOrDefault @Config @"cleanupPolicies" obj
     leiosVariant <- parseFieldOrDefault @Config @"leiosVariant" obj
+    leiosLateIbInclusion <- parseFieldOrDefault @Config @"leiosLateIbInclusion" obj
     leiosHeaderDiffusionTimeMs <- parseFieldOrDefault @Config @"leiosHeaderDiffusionTimeMs" obj
     praosChainQuality <- parseFieldOrDefault @Config @"praosChainQuality" obj
     simulateTransactions <- parseFieldOrDefault @Config @"simulateTransactions" obj
diff --git a/leios-trace-verifier/hs-src/test/Spec/Scenario.hs b/leios-trace-verifier/hs-src/test/Spec/Scenario.hs
index d311116b2..0fa8deb15 100644
--- a/leios-trace-verifier/hs-src/test/Spec/Scenario.hs
+++ b/leios-trace-verifier/hs-src/test/Spec/Scenario.hs
@@ -19,7 +19,7 @@ import qualified Data.Map.Strict as M
 import qualified Data.Set as S
 
 config :: Config
-config = Config{relayStrategy = RequestFromFirst, tcpCongestionControl = True, multiplexMiniProtocols = True, treatBlocksAsFull = False, cleanupPolicies = CleanupPolicies (S.fromList [CleanupExpiredVote]), simulateTransactions = True, leiosStageLengthSlots = 2, leiosStageActiveVotingSlots = 1, leiosVoteSendRecvStages = False, leiosVariant = Short, leiosHeaderDiffusionTimeMs = 1000.0, praosChainQuality = 20.0, txGenerationDistribution = Exp{lambda = 0.85, scale = pure 1000.0}, txSizeBytesDistribution = LogNormal{mu = 6.833, sigma = 1.127}, txValidationCpuTimeMs = 1.5, txMaxSizeBytes = 16384, rbGenerationProbability = 5.0e-2, rbGenerationCpuTimeMs = 1.0, rbHeadValidationCpuTimeMs = 1.0, rbHeadSizeBytes = 1024, rbBodyMaxSizeBytes = 90112, rbBodyLegacyPraosPayloadValidationCpuTimeMsConstant = 50.0, rbBodyLegacyPraosPayloadValidationCpuTimeMsPerByte = 5.0e-4, rbBodyLegacyPraosPayloadAvgSizeBytes = 0, ibGenerationProbability = 5.0, ibGenerationCpuTimeMs = 130.0, ibHeadSizeBytes = 304, ibHeadValidationCpuTimeMs = 1.0, ibBodyValidationCpuTimeMsConstant = 50.0, ibBodyValidationCpuTimeMsPerByte = 5.0e-4, ibBodyMaxSizeBytes = 327680, ibBodyAvgSizeBytes = 98304, ibDiffusionStrategy = FreshestFirst, ibDiffusionMaxWindowSize = 100, ibDiffusionMaxHeadersToRequest = 100, ibDiffusionMaxBodiesToRequest = 1, ibShards = 50, ebGenerationProbability = 1.5, ebGenerationCpuTimeMs = 75.0, ebValidationCpuTimeMs = 1.0, ebSizeBytesConstant = 240, ebSizeBytesPerIb = 32, ebDiffusionStrategy = PeerOrder, ebDiffusionMaxWindowSize = 100, ebDiffusionMaxHeadersToRequest = 100, ebDiffusionMaxBodiesToRequest = 1, ebMaxAgeSlots = 100, ebMaxAgeForRelaySlots = 40, voteGenerationProbability = 500.0, voteGenerationCpuTimeMsConstant = 0.164, voteGenerationCpuTimeMsPerIb = 0.0, voteValidationCpuTimeMs = 0.816, voteThreshold = 300, voteBundleSizeBytesConstant = 0, voteBundleSizeBytesPerEb = 105, voteDiffusionStrategy = PeerOrder, voteDiffusionMaxWindowSize = 100, voteDiffusionMaxHeadersToRequest = 100, voteDiffusionMaxBodiesToRequest = 1, certGenerationCpuTimeMsConstant = 90.0, certGenerationCpuTimeMsPerNode = 0.0, certValidationCpuTimeMsConstant = 130.0, certValidationCpuTimeMsPerNode = 0.0, certSizeBytesConstant = 7168, certSizeBytesPerNode = 0}
+config = Config{relayStrategy = RequestFromFirst, tcpCongestionControl = True, multiplexMiniProtocols = True, treatBlocksAsFull = False, cleanupPolicies = CleanupPolicies (S.fromList [CleanupExpiredVote]), simulateTransactions = True, leiosStageLengthSlots = 2, leiosStageActiveVotingSlots = 1, leiosVoteSendRecvStages = False, leiosVariant = Short, leiosLateIbInclusion = False, leiosHeaderDiffusionTimeMs = 1000.0, praosChainQuality = 20.0, txGenerationDistribution = Exp{lambda = 0.85, scale = pure 1000.0}, txSizeBytesDistribution = LogNormal{mu = 6.833, sigma = 1.127}, txValidationCpuTimeMs = 1.5, txMaxSizeBytes = 16384, rbGenerationProbability = 5.0e-2, rbGenerationCpuTimeMs = 1.0, rbHeadValidationCpuTimeMs = 1.0, rbHeadSizeBytes = 1024, rbBodyMaxSizeBytes = 90112, rbBodyLegacyPraosPayloadValidationCpuTimeMsConstant = 50.0, rbBodyLegacyPraosPayloadValidationCpuTimeMsPerByte = 5.0e-4, rbBodyLegacyPraosPayloadAvgSizeBytes = 0, ibGenerationProbability = 5.0, ibGenerationCpuTimeMs = 130.0, ibHeadSizeBytes = 304, ibHeadValidationCpuTimeMs = 1.0, ibBodyValidationCpuTimeMsConstant = 50.0, ibBodyValidationCpuTimeMsPerByte = 5.0e-4, ibBodyMaxSizeBytes = 327680, ibBodyAvgSizeBytes = 98304, ibDiffusionStrategy = FreshestFirst, ibDiffusionMaxWindowSize = 100, ibDiffusionMaxHeadersToRequest = 100, ibDiffusionMaxBodiesToRequest = 1, ibShards = 50, ebGenerationProbability = 1.5, ebGenerationCpuTimeMs = 75.0, ebValidationCpuTimeMs = 1.0, ebSizeBytesConstant = 240, ebSizeBytesPerIb = 32, ebDiffusionStrategy = PeerOrder, ebDiffusionMaxWindowSize = 100, ebDiffusionMaxHeadersToRequest = 100, ebDiffusionMaxBodiesToRequest = 1, ebMaxAgeSlots = 100, ebMaxAgeForRelaySlots = 40, voteGenerationProbability = 500.0, voteGenerationCpuTimeMsConstant = 0.164, voteGenerationCpuTimeMsPerIb = 0.0, voteValidationCpuTimeMs = 0.816, voteThreshold = 300, voteBundleSizeBytesConstant = 0, voteBundleSizeBytesPerEb = 105, voteDiffusionStrategy = PeerOrder, voteDiffusionMaxWindowSize = 100, voteDiffusionMaxHeadersToRequest = 100, voteDiffusionMaxBodiesToRequest = 1, certGenerationCpuTimeMsConstant = 90.0, certGenerationCpuTimeMsPerNode = 0.0, certValidationCpuTimeMsConstant = 130.0, certValidationCpuTimeMsPerNode = 0.0, certSizeBytesConstant = 7168, certSizeBytesPerNode = 0}
 
 topology :: Topology 'COORD2D
 topology = Topology{nodes = M.fromList [(NodeName "node-0", Node{nodeInfo = NodeInfo{stake = 500, cpuCoreCount = CpuCoreCount mzero, location = LocCoord2D{coord2D = Point{_1 = 0.12000040231003672, _2 = 0.1631004621065356}}, adversarial = mzero}, producers = M.fromList [(NodeName "node-1", LinkInfo{latencyMs = 141.01364015418432, bandwidthBytesPerSecond = BandwidthBps $ pure 1024000}), (NodeName "node-2", LinkInfo{latencyMs = 254.6249782835189, bandwidthBytesPerSecond = BandwidthBps $ pure 1024000})]}), (NodeName "node-1", Node{nodeInfo = NodeInfo{stake = 200, cpuCoreCount = CpuCoreCount mzero, location = LocCoord2D{coord2D = Point{_1 = 0.34276660615051174, _2 = 0.2636899791034371}}, adversarial = mzero}, producers = M.fromList [(NodeName "node-2", LinkInfo{latencyMs = 175.32530255486685, bandwidthBytesPerSecond = BandwidthBps $ pure 1024000}), (NodeName "node-3", LinkInfo{latencyMs = 379.1167948193313, bandwidthBytesPerSecond = BandwidthBps $ pure 1024000})]}), (NodeName "node-2", Node{nodeInfo = NodeInfo{stake = 100, cpuCoreCount = CpuCoreCount mzero, location = LocCoord2D{coord2D = Point{_1 = 0.5150493264153491, _2 = 0.27873594531347595}}, adversarial = mzero}, producers = M.fromList [(NodeName "node-3", LinkInfo{latencyMs = 248.31457793649423, bandwidthBytesPerSecond = BandwidthBps $ pure 1024000})]}), (NodeName "node-3", Node{nodeInfo = NodeInfo{stake = 0, cpuCoreCount = CpuCoreCount mzero, location = LocCoord2D{coord2D = Point{_1 = 0.3503537969220088, _2 = 0.13879558055660354}}, adversarial = mzero}, producers = M.fromList [(NodeName "node-0", LinkInfo{latencyMs = 140.19739576271448, bandwidthBytesPerSecond = BandwidthBps $ pure 1024000})]})]}
diff --git a/simulation/docs/SimulatorModel.md b/simulation/docs/SimulatorModel.md
index 5e3974ffd..1618b0388 100644
--- a/simulation/docs/SimulatorModel.md
+++ b/simulation/docs/SimulatorModel.md
@@ -96,7 +96,8 @@ Each EB (see `LeiosProtocol.Common.EndorseBlock`) consists of the following fiel
 
 More details for some fields.
 
-- An EB from iteration `i` includes the IDs of all IBs that were already adopted, are also from iteration `i`, and arrived before the end of `i`'s Deliver2 stage.
+- If `leios-late-ib-inclusion` is disabled, an EB from iteration `i` includes the IDs of all IBs that were already adopted, are also from iteration `i`, and arrived before the end of `i`'s Deliver2 stage.
+- If `leios-late-ib-inclusion` is enabled, an EB from iteration `i` includes the IDs of all IBs that were already adopted, are from an iteration `j` in the closed interval `[max 0 (i-2), i]`, and arrived before the end of `j`'s contemporary Deliver2 stage.
 - If the Leios variant is set to `short`, this EB includes no EB IDs.
 - If the Leios variant is set to `full`, an EB from iteration `i` includes the ID of the best eligible EB from each iteration with any eligible EBs.
     - An eligible EB has already been adopted, has already been certified, and is from an iteration in the closed interval `[i - min i (2 + pipelinesToReferenceFromEB), i-3]`.
@@ -129,8 +130,10 @@ More details for some fields.
 - A VB from iteration `i` includes the IDs of all EBs that satisfy the following.
     - The EB must have already been adopted.
     - The EB must also be from iteration `i`.
-    - The EB must only include IBs that have already been adopted, are from iteration `i`, and arrived before the end of `i`'s Endorse stage.
-    - The EB must include all IBs that have already been adopted, are from iteration `i`, and arrived before the end of `i`'s Deliver1 stage.
+    - If `leios-late-ib-inclusion` is disabled, the EB must only include IBs that have already been adopted, are from iteration `i`, and arrived before the end of `i`'s Endorse stage.
+    - If `leios-late-ib-inclusion` is disabled, the EB must include all IBs that have already been adopted, are from iteration `i`, and arrived before the end of `i`'s Deliver1 stage.
+    - If `leios-late-ib-inclusion` is enabled, the EB must only include IBs that have already been adopted, are from an iteration `j` in the closed interval `[max 0 (i-2), i]`, and arrived before the end of `j`'s Endorse stage.
+    - If `leios-late-ib-inclusion` is enabled, the EB must include all IBs that have already been adopted, are from an iteration `j` in the closed interval `[max 0 (i-2), i]`, and arrived before the end of `j`'s Deliver1 stage.
     - If the Leios variant is set to `full`, then let X be the EB's included EBs in iteration order; let Y be the EBs this node would have considered eligible if it were to retroactively create an EB for iteration `i` right now with the only extra restriction being ignore EBs that arrived within Δ_hdr of the end of iteration `i`; then `and (zipWith elem X Y)` must be `True`.
       (TODO the `zipWith` is suspicious; whether it would misbehave in various scenarios depends on many implementation details.)
 - The byte size is computed as `voteBundleSizeBytesConstant + voteBundleSizeBytesPerEb * #EBs` (which implies the weighted-vote perspective).
@@ -192,7 +195,7 @@ TODO discuss the other Relay parameters, backpressure, pipelining, etc?
 When an IB header arrives, its validation task is enqueued on the model CPU---for VBs and EBs it's just an ID, not a header, so there's no validation.
 Once that finishes, the Relay logic will decide whether it needs to fetch the body.
 
-- An IB body is not fetched if it's older than the slot to which the buffer as has already been pruned or if it's already in the buffer.
+- An IB body is not fetched if it exists earlier than it should, it's being offered later than it should be, or if it's already in the buffer.
 - An EB is not fetched if it's older than the slot to which the buffer has already been pruned, it's too old to be included by an RB (see `maxEndorseBlockAgeSlots`), or if it's already in the buffer.
 - A VB is not fetched if it's older than the slot to which the buffer has already been pruned or if it's already in the buffer.
 
@@ -233,7 +236,9 @@ Because those threads use STM to read both the state of pending tasks as well as
 
 The existence of those threads enable very simple logic for the adoption tasks.
 
-- The node adopts a validated IB by starting to diffuse it, adding its `UTCTime` arrival to `ibDeliveryTimesVar`, and removing the IB from the todo lists in `ibsNeededForEBVar`.
+- The node adopts a validated IB by starting to diffuse it, removing the IB from the todo lists in `ibsNeededForEBVar`, and recording its ID and which stage it arrived during.
+  See `iBsForEBsAndVotesVar`.
+  If it arrived during the IB's iteration's Propose stage (aka "early") or after the IB's iteration's Endorse stage (aka "tardy"), then the IB is discarded.
 - The node adopts a validated EB by starting to diffuse it, adding it to `relayEBState`, and adding a corresponding todo list of the not-already-available IBs to `ibsNeededForEBVar`.
 - The node adopts a validated VB by starting to diffuse it and adding it to `votesForEBVar`.
 - The node adopts a validated RB by starting to diffuse it and including it whenever calculating its selection; see `preferredChain`.
@@ -245,17 +250,18 @@ The Relay component invokes the given callback when some object arrives, and tha
 ## Pruning threads
 
 - *IBs 1*.
-  At the end of the Vote(Send) stage for iteration `i`, the node stops diffusing all IBs from `i`.
-  (TODO this should happen at the end of the Endorse stage, but this buffer is being abused as the adoption buffer as well.)
-  It also forgets any of those IBs it had adopted, with the exception of their arrival time, which is used when generating VBs.
+  At the end of the Endorse stage for iteration `i`, the node stops diffusing all IBs from `i`.
   See `relayIBState`.
+- *IBs 2*.
+  If `leios-late-ib-inclusion` is disabled, then at the end of the Vote(Send) stage for iteration `i`, the node forgets the arrival times of all IBs from `i`.
+  If `leios-late-ib-inclusion` is enabled, the node instead does that two stages later.
+  See `iBsForEBsAndVotesVar`.
 - *EBs 1*.
   At the end of the Vote(Recv) stage for iteration `i`, the node stops diffusing and completely forgets all EBs from `i` that are not already certified.
   See `relayEBState`, `votesForEBVar`, and `ibsNeededForEBVar`.
-- *VBs* and *IBs 2*.
+- *VBs*.
   At the end of the Vote(Recv) stage for iteration `i`, the node stops diffusing and completely forgets all VBs from `i`, except that certified EBs from `i` remember the ID and multiplicity of the VBs that first met quorum.
-  It also forgets the arrival time of IBs from `i`.
-  See `relayVoteState` and `ibDeliveryTimesVar`.
+  See `relayVoteState`.
 - *EBs 2*.
   If the Leios variant is set to `short`, then `maxEndorseBlockAgeSlots` after the end of the Endorse stage for iteration `i`, the node stops diffusing and forgets all EBs from `i` that were certified but are not included by an RB on the selected chain.
   (TODO these blocks should have stopped diffusing a long time ago, assuming `maxEndorseBlockAgeSlots >> sliceLength`)
@@ -281,7 +287,7 @@ TODO include `taskQueue`
 
 TODO `relayIBState` abuse
 
-TODO `ibDeliveryTimesVar`
+TODO `iBsForEBsAndVotesVar`
 
 ## Adopted EBs state
 
diff --git a/simulation/ouroboros-leios-sim.cabal b/simulation/ouroboros-leios-sim.cabal
index 62535694d..a6ddfee44 100644
--- a/simulation/ouroboros-leios-sim.cabal
+++ b/simulation/ouroboros-leios-sim.cabal
@@ -218,6 +218,7 @@ test-suite ols-test
     , bytestring
   other-modules:
     Paths_ouroboros_leios_sim
-    Test.Topology
     Test.Config
+    Test.ShortToFull
+    Test.Topology
   default-language: Haskell2010
diff --git a/simulation/src/LeiosProtocol/Relay.hs b/simulation/src/LeiosProtocol/Relay.hs
index 2042a6ed8..2fa3a0408 100644
--- a/simulation/src/LeiosProtocol/Relay.hs
+++ b/simulation/src/LeiosProtocol/Relay.hs
@@ -498,7 +498,7 @@ data SubmitPolicy = SubmitInOrder | SubmitAll
 
 data RelayConsumerConfig id header body m = RelayConsumerConfig
   { relay :: !RelayConfig
-  , shouldIgnore :: m (header -> Bool)
+  , shouldNotRequest :: m (header -> Bool)
   -- ^ headers to ignore, e.g. already received or coming too late.
   , validateHeaders :: [header] -> m ()
   , headerId :: !(header -> id)
@@ -761,7 +761,7 @@ relayConsumerPipelined config sst =
     if (min (Map.size lst0.available) (fromIntegral config.maxBodiesToRequest)) == 0
       then return (Left lst0)
       else return . Right . TS.Effect $ do
-        isIgnored <- config.shouldIgnore
+        isIgnored <- config.shouldNotRequest
         atomically $ do
           -- New headers are filtered before becoming available, but we have
           -- to filter `lst.available` again in the same STM tx that sets them as
@@ -987,7 +987,7 @@ relayConsumerPipelined config sst =
     m (RelayConsumerLocalState id header body n)
   acknowledgeIds lst idsSeq _ | Seq.null idsSeq = pure lst
   acknowledgeIds lst idsSeq idsMap = do
-    isIgnored <- config.shouldIgnore
+    isIgnored <- config.shouldNotRequest
     inFlight <- readTVarIO sst.inFlightVar
 
     let lst1 =
diff --git a/simulation/src/LeiosProtocol/Short.hs b/simulation/src/LeiosProtocol/Short.hs
index 7d9b35280..834e95eb8 100644
--- a/simulation/src/LeiosProtocol/Short.hs
+++ b/simulation/src/LeiosProtocol/Short.hs
@@ -111,6 +111,10 @@ data LeiosConfig = forall p. IsPipeline p => LeiosConfig
   , variant :: LeiosVariant
   , headerDiffusionTime :: NominalDiffTime
   -- ^ Δ_{hdr}.
+  , lateIbInclusion :: Bool
+  -- ^ Whether an EB also includes IBs from the two previous iterations.
+  --
+  -- TODO Merely one previous iteration if 'pipeline' is 'SingleVote'?
   , pipelinesToReferenceFromEB :: Int
   -- ^ how many older pipelines to reference from an EB when `variant = Full`.
   , votingFrequencyPerStage :: Double
@@ -147,6 +151,7 @@ convertConfig disk =
           , cleanupPolicies = disk.cleanupPolicies
           , variant = disk.leiosVariant
           , headerDiffusionTime = realToFrac $ durationMsToDiffTime disk.leiosHeaderDiffusionTimeMs
+          , lateIbInclusion = disk.leiosLateIbInclusion
           , pipelinesToReferenceFromEB =
               if disk.leiosVariant == Full
                 then
@@ -285,6 +290,7 @@ delaysAndSizesAsFull cfg@LeiosConfig{pipeline, voteSendStage} =
     , cleanupPolicies = cfg.cleanupPolicies
     , variant = cfg.variant
     , headerDiffusionTime = cfg.headerDiffusionTime
+    , lateIbInclusion = cfg.lateIbInclusion
     , pipelinesToReferenceFromEB = cfg.pipelinesToReferenceFromEB
     , activeVotingStageLength = cfg.activeVotingStageLength
     , votingFrequencyPerStage = cfg.votingFrequencyPerStage
@@ -461,21 +467,38 @@ isStage cfg stage slot = fromEnum slot >= cfg.sliceLength * fromEnum stage
 newtype PipelineNo = PipelineNo Word64
   deriving (Bounded, Enum, Show, Eq, Ord)
 
+pipelineMonus :: PipelineNo -> Word64 -> PipelineNo
+pipelineMonus (PipelineNo w) i = PipelineNo $ w - min w i
+
 stageRangeOf :: forall p. IsPipeline p => LeiosConfig -> PipelineNo -> Stage p -> (SlotNo, SlotNo)
 stageRangeOf cfg pl stage =
   fromMaybe
     undefined
     (stageRange cfg minBound (toEnum (fromEnum pl * cfg.sliceLength)) stage)
 
+-- | WARNING This fails if the slot is earlier than the beginning of the stage
+-- in the first iteration (ie @'PipelineNo' 0@)
 pipelineOf :: forall p. IsPipeline p => LeiosConfig -> Stage p -> SlotNo -> PipelineNo
 pipelineOf cfg stage sl =
-  toEnum $
-    fromMaybe undefined (fromEnum <$> stageStart cfg stage sl minBound)
-      `div` cfg.sliceLength
+  maybe err cnv $ stageStart cfg stage sl minBound
+ where
+  cnv = toEnum . (`div` cfg.sliceLength) . fromEnum
+
+  err = error $ show (cfg.sliceLength, x, stage, sl)
+
+  x :: String
+  x = case cfg of
+    LeiosConfig{pipeline} -> case pipeline of
+      SingSingleVote -> "SingleVote"
+      SingSplitVote -> "SplitVote"
 
 forEachPipeline :: (forall p. Stage p) -> (forall p. IsPipeline p => Stage p -> a) -> [a]
 forEachPipeline s k = [k @SingleVote s, k @SplitVote s]
 
+lastEndorse :: LeiosConfig -> PipelineNo -> SlotNo
+lastEndorse leios@LeiosConfig{pipeline = _ :: SingPipeline p} pipelineNo =
+  snd $ stageRangeOf @p leios pipelineNo Endorse
+
 lastVoteSend :: LeiosConfig -> PipelineNo -> SlotNo
 lastVoteSend leios@LeiosConfig{pipeline} pipelineNo = case pipeline of
   SingSingleVote -> snd (stageRangeOf leios pipelineNo Vote)
@@ -657,28 +680,76 @@ data EndorseBlocksSnapshot = EndorseBlocksSnapshot
   , certifiedEndorseBlocks :: (PipelineNo, PipelineNo) -> [(PipelineNo, [(EndorseBlock, Certificate, UTCTime)])]
   }
 
+-- | In which contemporary stage was an IB delivered
+--
+-- IBs cannot be deliver earlier than any of these options, due to the
+-- 'LeiosProtocol.Relay.shouldNotRequest' logic of the
+-- 'LeiosProtocol.Short.Node.relayIBState'.
+--
+-- IBs that are delivered later than any of these options are discarded,
+-- ignored.
+data IbDeliveryStage
+  = -- | The node will not vote for an EB that excludes IBs that arrived during
+    -- Propose or Deliver1.
+    --
+    -- The node will include IBs that arrived during Propose or Deliver1 in an
+    -- EB it makes.
+    IbDuringProposeOrDeliver1
+  | -- | The node will include IBs that arrived during Deliver2 in an EB it makes.
+    IbDuringDeliver2
+  | -- | The node will not vote for an EB that includes IBs that arrived later
+    -- than Endorse.
+    IbDuringEndorse
+  deriving (Bounded, Enum, Eq, Ord, Show)
+
 -- | Both constraints are inclusive.
 data InputBlocksQuery = InputBlocksQuery
-  { generatedBetween :: (SlotNo, SlotNo)
-  , receivedBy :: SlotNo
+  { generatedBetween :: (PipelineNo, PipelineNo)
+  , receivedBy :: IbDeliveryStage
   -- ^ This is checked against time the body is downloaded, before validation.
   }
 
+ibWasDeliveredLate :: LeiosConfig -> SlotConfig -> SlotNo -> UTCTime -> Bool
+ibWasDeliveredLate cfg slotCfg sl deliveryTime =
+  case ibDeliveryStage cfg slotCfg sl deliveryTime of
+    Nothing -> True
+    Just{} -> False
+
+ibDeliveryStage :: LeiosConfig -> SlotConfig -> SlotNo -> UTCTime -> Maybe IbDeliveryStage
+ibDeliveryStage
+  cfg@LeiosConfig{pipeline = _ :: SingPipeline p}
+  slotCfg
+  ibSlot
+  deliveryTime
+    | before loPropose = Nothing -- TODO future blocks?
+    | before loDeliver2 = Just IbDuringProposeOrDeliver1
+    | before loEndorse = Just IbDuringDeliver2
+    | before (succ hiEndorse) = Just IbDuringEndorse
+    | otherwise = Nothing -- TODO late blocks?
+   where
+    p = pipelineOf @p cfg Propose ibSlot
+
+    before sl = deliveryTime < slotTime slotCfg sl
+
+    (loPropose, _) = stageRangeOf @p cfg p Propose
+    (loDeliver2, _) = stageRangeOf @p cfg p Deliver2
+    (loEndorse, hiEndorse) = stageRangeOf @p cfg p Endorse
+
 inputBlocksToEndorse ::
   LeiosConfig ->
   -- | current slot
   SlotNo ->
   InputBlocksSnapshot ->
   [InputBlockId]
-inputBlocksToEndorse cfg@LeiosConfig{pipeline = _ :: SingPipeline p} current buffer = fromMaybe [] $ do
-  generatedBetween <- stageRange @p cfg Endorse current Propose
-  receivedBy <- stageEnd @p cfg Endorse current Deliver2
-  pure $
-    buffer.validInputBlocks
-      InputBlocksQuery
-        { generatedBetween
-        , receivedBy
-        }
+inputBlocksToEndorse cfg@LeiosConfig{pipeline = _ :: SingPipeline p} current buffer =
+  buffer.validInputBlocks
+    InputBlocksQuery
+      { generatedBetween = (lo, hi)
+      , receivedBy = IbDuringDeliver2
+      }
+ where
+  hi = pipelineOf @p cfg Endorse current
+  lo = if cfg.lateIbInclusion then pipelineMonus hi 2 else hi
 
 -- | Returns possible EBs to reference from current pipeline EB.
 endorseBlocksToReference ::
@@ -734,21 +805,24 @@ shouldVoteOnEB ::
 shouldVoteOnEB cfg@LeiosConfig{voteSendStage} _ slot _buffers _
   -- checks whether a pipeline has been started before.
   | Nothing <- stageRange cfg voteSendStage slot Propose = const False
-shouldVoteOnEB cfg@LeiosConfig{voteSendStage} slotConfig slot buffers ebuffers = cond
+shouldVoteOnEB cfg@LeiosConfig{voteSendStage = voteSendStage :: Stage p} slotConfig slot buffers ebuffers = cond
  where
-  generatedBetween = fromMaybe (error "impossible") $ stageRange cfg voteSendStage slot Propose
+  generatedBetween = (lo, hi)
+   where
+    hi = pipelineOf @p cfg voteSendStage slot
+    lo = if cfg.lateIbInclusion then pipelineMonus hi 2 else hi
   receivedByEndorse =
     buffers.validInputBlocks
       InputBlocksQuery
         { generatedBetween
-        , receivedBy = fromMaybe (error "impossible") $ stageEnd cfg voteSendStage slot Endorse
+        , receivedBy = IbDuringEndorse
         }
   receivedByDeliver1 = buffers.validInputBlocks q
    where
     q =
       InputBlocksQuery
         { generatedBetween
-        , receivedBy = fromMaybe (error "impossible") $ stageEnd cfg voteSendStage slot Deliver1
+        , receivedBy = IbDuringProposeOrDeliver1
         }
   -- Order of references in EndorseBlock matters for ledger state, so we stick to lists.
   -- Note: maybe order on (slot, subSlot, vrf proof) should be used instead?
diff --git a/simulation/src/LeiosProtocol/Short/Node.hs b/simulation/src/LeiosProtocol/Short/Node.hs
index 273686c3d..9c40dd3e0 100644
--- a/simulation/src/LeiosProtocol/Short/Node.hs
+++ b/simulation/src/LeiosProtocol/Short/Node.hs
@@ -19,7 +19,7 @@ import Control.Category ((>>>))
 import Control.Concurrent.Class.MonadMVar
 import Control.Concurrent.Class.MonadSTM.TSem
 import Control.Exception (assert)
-import Control.Monad (forever, guard, replicateM, when)
+import Control.Monad (forever, guard, replicateM, unless, when)
 import Control.Monad.Class.MonadAsync
 import Control.Monad.Class.MonadFork
 import Control.Monad.Class.MonadThrow
@@ -122,16 +122,29 @@ data LeiosNodeConfig = LeiosNodeConfig
 data LeiosNodeState m = LeiosNodeState
   { praosState :: !(PraosNode.PraosNodeState RankingBlockBody m)
   , relayIBState :: !(RelayIBState m)
-  , prunedIBStateToVar :: !(TVar m SlotNo)
+  -- ^ validated IBs that are still young enough to be diffusing
+  , iBsForEBsAndVotesVar :: !(TVar m (Map PipelineNo (Map InputBlockId IbDeliveryStage)))
+  -- ^ IBs that are relevant to an EB or Vote this node might need to issue
+  --
+  -- Each of these IBs arrived during its contemporary Propose, Deliver1,
+  -- Deliver2, or Endorse stages, has been validated, and is not too old.
+  --
+  -- INVARIANT: In basic Short Leios, none of these IBs are older than
+  -- @4*'sliceLength'@. With the @leios-late-ib-inclusion@ extension enabled,
+  -- none of these IBs are older than @(4+2)*'sliceLength'@.
+  --
+  -- Note that some IBs that are too old to be included in this variable
+  -- might still be needed in order to apply some RB.
+  --
+  -- INVARIANT: @all (\_k v -> not $ null v)@.
+  --
+  -- INVARIANT: @all (\k v -> all ((k ==) . pipelineOf cfg Propose) v)@.
   , relayEBState :: !(RelayEBState m)
   , prunedUnadoptedEBStateToVar :: !(TVar m SlotNo)
   , prunedUncertifiedEBStateToVar :: !(TVar m SlotNo)
   , relayVoteState :: !(RelayVoteState m)
   , prunedVoteStateToVar :: !(TVar m SlotNo)
   -- ^ TODO: refactor into RelayState.
-  , ibDeliveryTimesVar :: !(TVar m (Map InputBlockId (SlotNo, UTCTime)))
-  -- ^ records time we received the input block.
-  --   Also stores the SlotNo of the IB to ease pruning.
   , taskQueue :: !(TaskMultiQueue LeiosNodeTask m)
   , waitingForRBVar :: !(TVar m (Map (HeaderHash RankingBlock) [STM m ()]))
   -- ^ waiting for RB block itself to be validated.
@@ -186,7 +199,7 @@ data LedgerState = LedgerState
 
 data ValidationRequest m
   = ValidateRB !RankingBlock !(m ())
-  | ValidateIBS ![(InputBlockHeader, InputBlockBody)] !UTCTime !([(InputBlockHeader, InputBlockBody)] -> STM m ())
+  | ValidateIBs ![((InputBlockHeader, InputBlockBody), IbDeliveryStage)] !([(InputBlockHeader, InputBlockBody)] -> STM m ())
   | ValidateEBS ![EndorseBlock] !([EndorseBlock] -> STM m ())
   | ValidateVotes ![VoteMsg] !UTCTime !([VoteMsg] -> STM m ())
 
@@ -296,10 +309,10 @@ relayIBConfig _tracer cfg validateHeaders submitBlocks st =
     , maxHeadersToRequest = cfg.leios.ibDiffusion.maxHeadersToRequest
     , maxBodiesToRequest = cfg.leios.ibDiffusion.maxBodiesToRequest
     , submitBlocks
-    , shouldIgnore = atomically $ do
-        prunedTo <- readTVar st.prunedIBStateToVar
+    , shouldNotRequest = (getCurrentTime >>=) $ \deliveryTime -> atomically $ do
+        let late h = ibWasDeliveredLate cfg.leios cfg.slotConfig h.slot deliveryTime
         buff <- readTVar st.relayIBState.relayBufferVar
-        return $ \h -> h.slot < prunedTo || h.id `RB.member` buff
+        return $ \h -> late h || h.id `RB.member` buff
     }
 
 relayEBConfig ::
@@ -321,7 +334,7 @@ relayEBConfig _tracer cfg@LeiosNodeConfig{leios = LeiosConfig{pipeline = (_ :: S
     , maxBodiesToRequest = cfg.leios.ebDiffusion.maxBodiesToRequest
     , submitBlocks = \hbs t k ->
         submitBlocks (map (first (.id)) hbs) t (k . map (\(i, b) -> (RelayHeader i b.slot, b)))
-    , shouldIgnore = do
+    , shouldNotRequest = do
         -- We possibly prune certified EBs (not referenced in the
         -- chain) after maxEndorseBlockAgeSlots, so we should not end
         -- up asking for their bodies again, in the remote possibility
@@ -362,7 +375,7 @@ relayVoteConfig _tracer cfg submitBlocks _ leiosState =
     , maxBodiesToRequest = cfg.leios.voteDiffusion.maxBodiesToRequest
     , submitBlocks = \hbs t k ->
         submitBlocks (map (first (.id)) hbs) t (k . map (\(i, b) -> (RelayHeader i b.slot, b)))
-    , shouldIgnore = atomically $ do
+    , shouldNotRequest = atomically $ do
         buffer <- readTVar leiosState.relayVoteState.relayBufferVar
         prunedTo <- readTVar leiosState.prunedVoteStateToVar
         return $ \hd ->
@@ -389,13 +402,12 @@ newLeiosNodeState ::
 newLeiosNodeState cfg = do
   praosState <- PraosNode.newPraosNodeState cfg.baseChain
   relayIBState <- newRelayState
-  prunedIBStateToVar <- newTVarIO (toEnum 0)
+  iBsForEBsAndVotesVar <- newTVarIO Map.empty
   relayEBState <- newRelayState
   prunedUnadoptedEBStateToVar <- newTVarIO (toEnum 0)
   prunedUncertifiedEBStateToVar <- newTVarIO (toEnum 0)
   relayVoteState <- newRelayState
   prunedVoteStateToVar <- newTVarIO (toEnum 0)
-  ibDeliveryTimesVar <- newTVarIO Map.empty
   ibsNeededForEBVar <- newTVarIO Map.empty
   ledgerStateVar <- newTVarIO Map.empty
   waitingForRBVar <- newTVarIO Map.empty
@@ -432,7 +444,9 @@ leiosNode tracer cfg followers peers = do
   let submitRB rb completion = dispatch $! ValidateRB rb completion
   let submitIB xs deliveryTime completion = do
         traceReceived xs $ EventIB . uncurry InputBlock
-        dispatch $! ValidateIBS xs deliveryTime completion
+        let annotate x = (,) x <$> ibDeliveryStage cfg.leios cfg.slotConfig (fst x).slot deliveryTime
+        let xs' = mapMaybe annotate xs -- TODO what to do with early/late arrivals?
+        unless (null xs') $ dispatch $! ValidateIBs xs' completion
   let submitVote (map snd -> xs) deliveryTime completion = do
         traceReceived xs EventVote
         dispatch $! ValidateVotes xs deliveryTime $ completion . map (\v -> (v.id, v))
@@ -516,7 +530,10 @@ leiosNode tracer cfg followers peers = do
             -- TODO: could expire EBs not referenced by young enough EBs.
             cfg.leios.variant /= Full
             ]
-          , [ pruneExpiredIBs tracer cfg leiosState
+          , [ pruneRelayIBState tracer cfg leiosState
+            | CleanupExpiredIb `isEnabledIn` cfg.leios.cleanupPolicies
+            ]
+          , [ pruneIBsForEBsAndVotesVar tracer cfg leiosState
             | CleanupExpiredIb `isEnabledIn` cfg.leios.cleanupPolicies
             ]
           ]
@@ -533,17 +550,15 @@ leiosNode tracer cfg followers peers = do
       , pruningThreads
       ]
 
--- Actually prunes IBs we should stop delivering.
-pruneExpiredIBs :: (Monad m, MonadDelay m, MonadSTM m, MonadTime m) => Tracer m LeiosNodeEvent -> LeiosNodeConfig -> LeiosNodeState m -> m ()
-pruneExpiredIBs _tracer LeiosNodeConfig{leios, slotConfig} st = go (toEnum 0)
+-- Prunes 'relayIBState'
+pruneRelayIBState :: (Monad m, MonadDelay m, MonadSTM m, MonadTime m) => Tracer m LeiosNodeEvent -> LeiosNodeConfig -> LeiosNodeState m -> m ()
+pruneRelayIBState _tracer LeiosNodeConfig{leios, slotConfig} st = go (toEnum 0)
  where
   go p = do
-    -- TODO: could end when Endorse ends, but we want them around for voting.
-    let endOfIBDiffusion = succ $ lastVoteSend leios p
+    let expiry = succ $ lastEndorse leios p
     let pruneTo = succ $ snd $ proposeRange leios p
-    _ <- waitNextSlot slotConfig endOfIBDiffusion
+    _ <- waitNextSlot slotConfig expiry
     _ibsPruned <- atomically $ do
-      writeTVar st.prunedIBStateToVar $! pruneTo
       partitionRBVar st.relayIBState.relayBufferVar $
         \ibEntry -> (fst ibEntry.value).slot < pruneTo
     -- TODO: batch these, too many events
@@ -551,6 +566,19 @@ pruneExpiredIBs _tracer LeiosNodeConfig{leios, slotConfig} st = go (toEnum 0)
     --   traceWith tracer $! LeiosNodeEvent Pruned (EventIB ib)
     go (succ p)
 
+pruneIBsForEBsAndVotesVar :: (Monad m, MonadDelay m, MonadSTM m, MonadTime m) => Tracer m LeiosNodeEvent -> LeiosNodeConfig -> LeiosNodeState m -> m ()
+pruneIBsForEBsAndVotesVar _tracer LeiosNodeConfig{leios, slotConfig} st = go (toEnum 0)
+ where
+  go p = do
+    let expiry = succ $ lastVoteSend leios $ (if leios.lateIbInclusion then succ . succ else id) $ p
+    _ <- waitNextSlot slotConfig expiry
+    _ibsPruned <- atomically $ do
+      modifyTVar'
+        st.iBsForEBsAndVotesVar
+        (snd . Map.split p)
+    -- TODO Pruned events
+    go (succ p)
+
 -- rEB slots after the end of Endorse,
 -- prune EBs that became certified but were not adopted by an RB.
 pruneExpiredUnadoptedEBs ::
@@ -665,13 +693,10 @@ pruneExpiredVotes ::
 pruneExpiredVotes _tracer LeiosNodeConfig{leios = leios@LeiosConfig{pipeline = _ :: SingPipeline p}, slotConfig} st = go (toEnum 0)
  where
   go p = do
-    let pruneIBDeliveryTo = succ $ snd (stageRangeOf @p leios p Short.Propose)
     let pruneTo = succ (lastVoteSend leios p)
     _ <- waitNextSlot slotConfig (succ (lastVoteRecv leios p))
     _votesPruned <- atomically $ do
       writeTVar st.prunedVoteStateToVar $! pruneTo
-      -- delivery times for IBs are only needed to vote, so they can be pruned too.
-      modifyTVar' st.ibDeliveryTimesVar $ Map.filter $ \(slot, _) -> slot >= pruneIBDeliveryTo
       partitionRBVar st.relayVoteState.relayBufferVar $
         \voteEntry ->
           let voteSlot = (snd voteEntry.value).slot
@@ -782,20 +807,27 @@ validateIBsOfCertifiedEBs _trace _cfg st = forever . atomically $ do
     modifyTVar' st.ibsValidationActionsVar $ Map.delete ibId
     m
 
-adoptIB :: MonadSTM m => LeiosNodeState m -> InputBlock -> UTCTime -> STM m ()
-adoptIB leiosState ib deliveryTime = do
+-- | This is called once the IB has been validated
+--
+-- An IB might be validated a long while after it arrived.
+--
+-- An IB that arrived later than it should have will not even be validated.
+adoptIB :: MonadSTM m => LeiosConfig -> LeiosNodeState m -> InputBlock -> IbDeliveryStage -> STM m ()
+adoptIB cfg leiosState ib deliveryStage = do
   let !ibSlot = ib.header.slot
-  -- NOTE: voting relies on delivery times for IBs
+      !p = case cfg of
+        LeiosConfig{pipeline = _ :: SingPipeline p} ->
+          pipelineOf @p cfg Short.Propose ibSlot
   modifyTVar'
-    leiosState.ibDeliveryTimesVar
-    (Map.insertWith (\(_, x) (s, y) -> (,) s $! min x y) ib.id (ibSlot, deliveryTime))
+    leiosState.iBsForEBsAndVotesVar
+    (Map.insertWith (Map.unionWith min) p $ Map.singleton ib.id deliveryStage)
 
   -- TODO: likely needs optimization, although EBs also grow slowly.
   modifyTVar' leiosState.ibsNeededForEBVar (Map.map (Set.delete ib.id))
 
 adoptEB :: MonadSTM m => LeiosNodeState m -> EndorseBlock -> STM m ()
 adoptEB leiosState eb = do
-  ibs <- RB.keySet <$> readTVar leiosState.relayIBState.relayBufferVar
+  ibs <- Set.unions . Map.map Map.keysSet <$> readTVar leiosState.iBsForEBsAndVotesVar
   let ibsNeeded = Map.fromList [(eb.id, Set.fromList eb.inputBlocks Set.\\ ibs)]
   modifyTVar' leiosState.ibsNeededForEBVar (`Map.union` ibsNeeded)
 
@@ -821,12 +853,12 @@ dispatchValidation tracer cfg leiosState req =
   valRB rb m = do
     let task prefix = cpuTask prefix cfg.leios.praos.blockValidationDelay rb
     labelTask (ValRB, (task, m))
-  valIB x@(uncurry InputBlock -> ib) deliveryTime completion =
+  valIB x@(uncurry InputBlock -> ib) deliveryStage completion =
     let
       delay prefix = cpuTask prefix cfg.leios.delays.inputBlockValidation ib
       task = atomically $ do
         completion [x]
-        adoptIB leiosState ib deliveryTime
+        adoptIB cfg.leios leiosState ib deliveryStage
      in
       labelTask (ValIB, (delay, task >> traceEnterState [uncurry InputBlock x] EventIB))
   valEB eb completion = labelTask . (ValEB,) . (\p -> cpuTask p cfg.leios.delays.endorseBlockValidation eb,) $ do
@@ -856,7 +888,7 @@ dispatchValidation tracer cfg leiosState req =
                     else leiosState.waitingForLedgerStateVar
           waitFor var [(prev, [queue [task]])]
           return []
-    ValidateIBS ibs deliveryTime completion -> do
+    ValidateIBs ibs completion -> do
       -- NOTE: IBs with an RB reference have to wait for ledger state of that RB.
       --       However, if they get referenced by the chain they should be validated anyway.
       --       We use a map to store the validation logic, so we can force it happening in the latter case.
@@ -868,14 +900,14 @@ dispatchValidation tracer cfg leiosState req =
                   Map.delete ibId
                 m
               Nothing -> pure ()
-      let storeAction rbHash ib@(h, _) = do
+      let storeAction rbHash ib@(h, _) deliveryStage = do
             modifyTVar' leiosState.ibsValidationActionsVar $
-              Map.insert h.id (queue [valIB ib deliveryTime completion])
+              Map.insert h.id (queue [valIB ib deliveryStage completion])
             return (rbHash, [lookupValAction $ (fst ib).id])
       waitingLedgerState <-
         sequence $
-          [ storeAction rbHash ib
-          | ib <- ibs
+          [ storeAction rbHash ib deliveryStage
+          | (ib, deliveryStage) <- ibs
           , BlockHash rbHash <- [(fst ib).rankingBlock]
           ]
 
@@ -884,7 +916,7 @@ dispatchValidation tracer cfg leiosState req =
         leiosState.waitingForLedgerStateVar
         waitingLedgerState
 
-      return [valIB ib deliveryTime completion | ib@(h, _) <- ibs, GenesisHash <- [h.rankingBlock]]
+      return [valIB ib deliveryStage completion | (ib@(h, _), deliveryStage) <- ibs, GenesisHash <- [h.rankingBlock]]
     ValidateEBS ebs completion -> do
       -- NOTE: block references are only inspected during voting.
       return [valEB eb completion | eb <- ebs]
@@ -922,10 +954,10 @@ generator tracer cfg st = do
           traceWith tracer (PraosNodeEvent (PraosNodeEventGenerate rb))
           traceWith tracer (PraosNodeEvent (PraosNodeEventNewTip newChain))
         SomeAction Generate.Propose{} ib -> (GenIB,) $ do
-          now <- getCurrentTime
           atomically $ do
+            -- TODO should not be added to 'relayIBState' before it's validated
             modifyTVar' st.relayIBState.relayBufferVar (RB.snocIfNew ib.header.id (ib.header, ib.body))
-            adoptIB st ib now
+            adoptIB cfg.leios st ib IbDuringProposeOrDeliver1
           traceWith tracer (LeiosNodeEvent Generate (EventIB ib))
         SomeAction Generate.Endorse eb -> (GenEB,) $ do
           atomically $ do
@@ -952,7 +984,6 @@ mkBuffersView cfg st = BuffersView{..}
     chain <- PraosNode.preferredChain st.praosState
     bufferEB <- readTVar st.relayEBState.relayBufferVar
     votesForEB <- readTVar st.votesForEBVar
-    ibsNeededForEB <- readTVar st.ibsNeededForEBVar
     -- RBs in the same chain should not contain certificates for the same pipeline.
     let pipelinesInChain =
           Set.fromList $
@@ -964,9 +995,6 @@ mkBuffersView cfg st = BuffersView{..}
     let tryCertify eb = do
           Certified{cert} <- Map.lookup eb.id votesForEB
           guard (not $ Set.member (endorseBlockPipeline cfg.leios eb) pipelinesInChain)
-          -- Note: we expect to have received the IBs for any
-          -- certified EB, but degraded network could mean we do not.
-          guard (Map.lookup eb.id ibsNeededForEB == Just Set.empty)
           return $! (eb.id,) $! cert
 
     -- TODO: cache index of EBs ordered by .slot?
@@ -995,20 +1023,25 @@ mkBuffersView cfg st = BuffersView{..}
     let txsPayload = cfg.leios.sizes.inputBlockBodyAvgSize
     return $ NewInputBlockData{referenceRankingBlock, txsPayload}
   ibs = do
-    buffer <- readTVar st.relayIBState.relayBufferVar
-    times <- readTVar st.ibDeliveryTimesVar
-    let generatedCheck r =
-          map (.id)
-            . filter (\ib -> ib.slot `inRange` r)
-            . map fst
-            . RB.values
-            $ buffer
-        receivedByCheck slot =
-          filter
-            ( maybe False ((<= slotTime cfg.slotConfig slot) . snd)
-                . flip Map.lookup times
-            )
-        validInputBlocks q = receivedByCheck q.receivedBy $ generatedCheck q.generatedBetween
+    let splitLE k m =
+          let (lt, mbEq, _gt) = Map.splitLookup k m
+           in case mbEq of
+                Nothing -> lt
+                Just eq -> Map.insert k eq lt
+        splitGE k m =
+          let (_lt, mbEq, gt) = Map.splitLookup k m
+           in case mbEq of
+                Nothing -> gt
+                Just eq -> Map.insert k eq gt
+        generatedCheck (lo, hi) =
+          Map.unions
+            . splitGE lo
+            . splitLE hi
+        receivedByCheck hi =
+          mapMaybe (\(ibId, deliveryStage) -> do guard (deliveryStage <= hi); Just ibId)
+            . Map.toList
+    xs <- readTVar st.iBsForEBsAndVotesVar
+    let validInputBlocks q = receivedByCheck q.receivedBy . generatedCheck q.generatedBetween $ xs
     return InputBlocksSnapshot{..}
   ebs = do
     buffer <- readTVar st.relayEBState.relayBufferVar
diff --git a/simulation/src/LeiosProtocol/Short/Sim.hs b/simulation/src/LeiosProtocol/Short/Sim.hs
index 6efd57392..0d3f4f884 100644
--- a/simulation/src/LeiosProtocol/Short/Sim.hs
+++ b/simulation/src/LeiosProtocol/Short/Sim.hs
@@ -427,6 +427,7 @@ traceRelayLink1 connectionOptions =
               , cleanupPolicies = def
               , variant = Short
               , headerDiffusionTime = 1
+              , lateIbInclusion = False
               , pipelinesToReferenceFromEB = 0
               , activeVotingStageLength = 1
               , pipeline = SingSingleVote
diff --git a/simulation/src/LeiosProtocol/SimTestRelay.hs b/simulation/src/LeiosProtocol/SimTestRelay.hs
index 6eeea453a..86b7684a9 100644
--- a/simulation/src/LeiosProtocol/SimTestRelay.hs
+++ b/simulation/src/LeiosProtocol/SimTestRelay.hs
@@ -138,7 +138,7 @@ relayNode
     let relayConsumerConfig =
           RelayConsumerConfig
             { relay = relayConfig
-            , shouldIgnore = atomically $ do
+            , shouldNotRequest = atomically $ do
                 rb <- readTVar relayBufferVar
                 return $ \hd -> RB.member (testHeaderId hd) rb
             , -- sequential validation of headers
diff --git a/simulation/test/Main.hs b/simulation/test/Main.hs
index 0969f5796..25ce1f8c1 100644
--- a/simulation/test/Main.hs
+++ b/simulation/test/Main.hs
@@ -1,6 +1,7 @@
 module Main where
 
 import qualified Test.Config
+import qualified Test.ShortToFull
 import Test.Tasty (defaultMain, testGroup)
 import qualified Test.Topology
 
@@ -9,4 +10,5 @@ main =
   defaultMain . testGroup "ouroboros-leios-sim" $
     [ Test.Topology.tests
     , Test.Config.tests
+    , Test.ShortToFull.tests
     ]
diff --git a/simulation/test/Test/ShortToFull.hs b/simulation/test/Test/ShortToFull.hs
new file mode 100644
index 000000000..9f9b47103
--- /dev/null
+++ b/simulation/test/Test/ShortToFull.hs
@@ -0,0 +1,85 @@
+{-# LANGUAGE OverloadedRecordDot #-}
+{-# LANGUAGE ParallelListComp #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+
+module Test.ShortToFull where
+
+import Data.Default (def)
+import Data.List (sort)
+import LeiosProtocol.Common (InputBlockId (..), NodeId (..), SlotNo)
+import LeiosProtocol.Config (Config)
+import qualified LeiosProtocol.Short as Short
+import Test.QuickCheck as Q
+import Test.Tasty (TestTree, testGroup)
+import Test.Tasty.QuickCheck (testProperty)
+
+tests :: TestTree
+tests =
+  testGroup
+    "ShortToFull"
+    [ testProperty "test_leiosLateIbInclusion" test_leiosLateIbInclusion
+    ]
+
+data Test_leiosLateIbInclusion = Test_leiosLateIbInclusion
+  { ibTable :: [(Int, Short.PipelineNo, Short.IbDeliveryStage)] -- the Int is @zip [0..]@, /before shrinking/
+  , ebLo :: SlotNo
+  -- ^ this first slot in which an EB could actually exist
+  , ebSlot :: SlotNo
+  }
+  deriving (Show)
+
+instance Q.Arbitrary Test_leiosLateIbInclusion where
+  arbitrary = do
+    let cfg = Short.convertConfig def
+    let (ebLo, ebHi) = case cfg of
+          Short.LeiosConfig{pipeline = _ :: Short.SingPipeline p} ->
+            Short.stageRangeOf @p cfg (toEnum 0) Short.Endorse
+    ebSlot <- toEnum <$> Q.choose (fromEnum ebLo, fromEnum ebHi + 9 * cfg.sliceLength)
+    ibTable <- do
+      n <- Q.choose (0, 1000)
+      gens <- Q.vectorOf n $ fmap toEnum $ Q.choose (0, 20)
+      delays <- Q.vectorOf n $ Q.elements [minBound .. maxBound]
+      pure $ [(i, gen, delay) | i <- [0 ..] | gen <- sort gens | delay <- delays]
+    pure Test_leiosLateIbInclusion{..}
+
+  shrink testSetup =
+    [ testSetup{ibTable = ibTable'}
+    | ibTable' <- shrinkList (const []) testSetup.ibTable
+    ]
+
+test_leiosLateIbInclusion :: Test_leiosLateIbInclusion -> Property
+test_leiosLateIbInclusion testSetup =
+  Q.counterexample (show (cfg.sliceLength, iterations))
+    $ Q.counterexample ("ebPipeline " <> show (fromEnum ebSlot `div` cfg.sliceLength))
+    $ Q.counterexample ("on " <> show (map (.num) on))
+    $ Q.counterexample
+      (unlines $ ("off" :) $ map (show . map (.num) . off) $ iterations)
+    $ on Q.=== concatMap off iterations
+ where
+  Test_leiosLateIbInclusion{..} = testSetup
+  cfg = Short.convertConfig def
+  ibSnapshot =
+    Short.InputBlocksSnapshot
+      { validInputBlocks = \q ->
+          [ InputBlockId{node = NodeId 0, num = i}
+          | (i, gen, recv) <- ibTable
+          , gen `Short.inRange` q.generatedBetween
+          , recv <= q.receivedBy
+          ]
+      }
+  on =
+    Short.inputBlocksToEndorse
+      cfg{Short.lateIbInclusion = True}
+      ebSlot
+      ibSnapshot
+  off sl =
+    Short.inputBlocksToEndorse
+      cfg{Short.lateIbInclusion = False}
+      sl
+      ibSnapshot
+  iterations =
+    let capL = fromIntegral cfg.sliceLength
+     in -- discard underflow and negative iterations
+        dropWhile (\sl -> sl > ebSlot || sl < ebLo) [ebSlot - 2 * capL, ebSlot - capL, ebSlot]