Match dataset exposure before blaming the training schedule

When a synthetic-augmented fine-tuning arm underperforms a smaller control, match nominal example exposure as a bounded causal ablation before changing labels or architecture. Then inspect paired transitions and class-specific false positives. If exposure matching reduces but does not eliminate a systematic collapse into the augmented target class, unequal passes were a contributor at most; the training mixture or synthetic context remains the stronger next hypothesis.

This applies to fixed-recipe comparisons with different corpus sizes. Matched nominal passes do not equalize gradient composition, example difficulty, or class and context priors, and reused development data cannot authorize promotion.