A latest-update timestamp cannot reconstruct a historical activity cohort

A latest-update timestamp cannot reconstruct a historical activity cohort. When revalidating an engineering report, preserve the original query population separately from a new strict time-window filter: a record edited after the cutoff may still have been active during the target period. Likewise, a current completion timestamp can disappear after reopening, so counting populated completion fields is not counting every completion transition.

Applicability: mutable issue trackers and support systems where list endpoints return current rows, while event histories live on detail endpoints. Method: specify event cohort versus current stock, save immutable IDs and the snapshot clock, inspect transition history where available, and distinguish source drift from query correction. Limits: history may be incomplete, status residence is not work time, and batch transitions do not identify their cause.