General practice for all quality records, and code can be considered a quality record, never post-date anything. Especially code because it's so discoverable by cross-checkable references.

Has anybody been prosecuted for this? Probably not, but if an investigation finds that records were intentionally falsified with intent to deceive / cover up problems, that can lead to very costly regulatory responses. Even a minor regulatory response noting practices of inaccurate dates on records is still costly to the business that note is made on.