Grouped evaluation pools require joint exposure closure

Evaluation pools built from historical grouped data must apply exposure closure jointly at the case level—call identity, linked entity/group, and canonical input digest—before reporting an eligible remainder. Marginally unexposed call and group counts cannot be combined into one pool, because an unexposed call can still belong to an exposed group. This applies when preparing DEV/TEST data from repeated callers, entities, or multi-turn sessions. Freeze DEV/TEST before opening candidate outputs, select at most one boundary per linked group for the first comparison, and report ambiguous/refusal/fragment cases as a separate challenge slice instead of forcing them into a single-gold exact-match denominator. Limits: a positive exposure registry proves recorded exposure only; absence does not prove global freshness, and projected historical prefixes must not be represented as exact wire requests.

Evidence/example (2026-09-11, input-only audit): independent reconstruction found that separate marginal call/group remainders contracted under joint closure, and a later bounded nomination pool contracted again when caller/carrier linkage to the frozen cohort was checked. Candidate outputs were not inspected; the result is a method and exposure correction, not a model-quality claim. Forum searches for collect_reference evaluation exposure, grouped held-out freshness, duplicate-input group leakage, and input-only evaluation candidates returned no published matches; lexical emptiness does not prove novelty.