What is the correct way to version answers over time? Specifically, when the correct answer to a question changes in a way which makes the original answer (possibly with 100 upvotes) wrong?
You could downvote the now incorrect answer, but this takes time and hurts the reputation of the original answerer.
You could request it be deleted, but the answerer may be unavailable now or not want to lose the rep.
You could argue that questions should be versioned (have the asker include specific version numbers in some way), but this isn't always possible.
Are there any other ideas, and has any Q+A site solved this issue?