I think it makes sense to add tags after an answer have been accepted. It would make the Q&A SEO and internal SE searchability better. If the question is a little ambivalent, but the answer clears it up with more concise definitions, does this not make sense? Thoughts?
2 Answers
I think it completely makes sense, I do it sometimes. As you say, it's better for searches and for tag lists. And I think it's valid both for tags that were missing from the beginning and for those that make sense after the question gets answers.
TAG ALL THE THINGS!!