Preferably, when closing a duplicate, this happens before any answers have been given to the dupe-to-be. However, it can happen that only after editing of the question and multiple answers, it turns out that it's actually a duplicate.
Should we then always vote to close the newer question as a duplicate, or should we try to keep the better question (or the question with the better answers) and vote to close the other question, even if that is the older one?
An example: we have the questions "What's the significance of this passage from “The Goblet of Fire”?" and "Why was Dumbledore worried by the cut in Harry's arm?".
The latter was asked about two months after the former. And while the OP of the latter insisted that his question was specifically about the cut itself, rather than the fact that Voldemort used Harry's blood, the accepted answers are very much the same, which makes them duplicates.
But which one should we close?
Both have good answers, but I think the answer in the second question is more complete than the answer to the first one, so I would prefer vote to close the older question as a duplicate of the newer one.
Or are there other options, such as merging? (I've only read about it, I've never seen it happen; it seems uncommon).