A memory can answer a current query correctly while discarding distinctions required by a later update.
We investigate this failure with a paired-history audit: two histories have the same current answer, receive a shared future update, and require different subsequent answers.
A pilot evaluation
A pilot evaluates 24 history pairs across six synthetic mechanisms, 12 memory conditions, two repeats, and two model backends.
Results
A deterministic frontier selector obtains strict reveal accuracy of 96/96 on DeepSeek and 82/96 on GLM; a structured writer obtains 62 successes with one unresolved outcome and 56/96.
The configured four-outcome joint contrast has finite-sample identification intervals of [0.521, 0.542] and [0.292, 0.313], not confidence intervals.
A record-level audit
A record-level audit distinguishes retained-state adequacy, response delivery, and answer-schema compliance without changing those original scores.
It finds 26 and 25 well-formed but semantically wrong structured reveal memories, while all 14 GLM frontier reveal failures contain correct values in the wrong wrapper.
Tombstone removal
Tombstone removal produces 16/16 exact replay failures in the targeted mechanism.
Identifier renaming then exposes a separate flaw: original frontier late-reference adequacy falls from 8/8 to 94/320 transformed instances.
Label-equivariant repair
We provide and test a label-equivariant repair, but it preserves only 2/8 original late-reference answers: eliminating a naming shortcut does not solve unknown future relevance.
Methodology and validation
These results support a scoped evaluation methodology and reproducible failure analysis, not general superiority of the repaired algorithm.
Paid pilot evidence, retrospective diagnostics, and new offline tests are reported separately; no independent held-out or natural-task validation is claimed.