Find exactly what changed
A witness may correct a date while retaining the event, identify a person more carefully or withdraw a detail they no longer trust. Treat the correction at the level it actually affects. A changed minute does not necessarily invalidate every observation, and an apparently minor identity correction may matter a great deal. Compare the versions directly rather than relying on the impression that the story changed.
Worked example: the evening visit
A witness first says Monday, then says Tuesday after checking a work rota. The rota provides a stated reason for the revision. You should still evaluate whether it supports the corrected date, but the correction itself is not proof of deception. It may show the witness distinguishing unaided recollection from a record-based check.
Retain both versions
Keep the original claim, the corrected claim and the reason given for the change. Look for independent evidence that favors one version or leaves both unresolved. In Somatry, a revised statement can be significant without becoming a shortcut to guilt. The important question is whether the change fits the records and alters your theory, not whether a fictional person has remembered every detail perfectly on the first attempt.