Recently, What was the first movie to feature zombie babies? was changed from a list question to a question about which the first case was. There was already an answer that indicated two movies that had zombie children that had 5 upvotes and an accept. Because of the question change, the answer is no longer correct. How should this be handled? Should the correct answer be amended to answer the question (possible without removing information, but requiring adding a little)?
Why did this happen in the first place?
This happened because the original question was off-topic. "Are there any movies with X" questions are generally regarded as open-ended list questions.
Shortly after it was posted, it was closed by moderator @Pearsonartphoto as "Not Constructive" which at the time served as a proxy for list question closures.
In the intervening days between being posted and being closed, however, the question was answered by @Spectre. This is where the problem occurred. Since this was a list question, it never should have been answered. It should have been closed promptly by the community or by a moderator.
Not all questions can or should be answered here. Save yourself some frustration and avoid trying to answer questions which... [etc...]
Now that it has been edited and re-opened, the original answer is now not a good match to the original question.
So, what should be done?
In my opinion, editing Spectre's answer would not be appropriate since you would be changing the intention of what he put.
The old question should be closed, left closed and a new question should be asked rather than attempting to write an entirely new question to evade the original (historic) close.