What do we do when there are duplicate questions that get missed?

Question

What do we do when duplicate questions go missed, both questions have good answers (full disclosure: I answered one of the questions in question), and both have been established and open for some time? This question was asked back in October and received some answers, and this one was asked just about a month ago (particularly disappointing because I recall thinking there was a duplicate when I answered it and couldn't find one!).

I flagged the earlier one as a duplicate because it came up in the activity feed this afternoon when it received a new answer and I incorrectly perceived it as being a new question, so I voted to close as a duplicate. As @Miniman pointed out in the comments on that question, we generally don't close the older of the two questions when there are duplicates, but it also doesn't feel right to close the newer one, being that it's been open for a month now.

If the general policy is to simply vote to close the more recent one, that's fine, but might it make more sense to merge the questions? I'm probably overthinking this and will go and vote to close the latter one as a duplicate anyway. Anyway, what do?

Answer 1

Mods have access to the merge action, which moves all answers from one question to the master question, closes the duplicate as a duplicate (if it hasn't been already), and then locks the duplicate to make sure the connection “sticks” and can't be undone by voting.

So in practice, how we handle missed duplicates that have already collected substantial answers is to wait for a duplicate close to happen and “settle” — that is, get the chance to be contested, have clarifications happen, or whatever until its open/closed status looks solid — and then someone can custom flag it and ask a mod to do a merge.

Doing it this way takes longer than it might otherwise, but the plus side is that it avoids irrecoverably moving answers before it's 100% certain to be the correct course of action.

Answer 2

While @SevenSidedDie already answered the main question, I would like to make an observation: Age does not matter.

StackExchange does not live by the First Come, First Serve principle, but instead aims at providing quality answers to questions.

The idea behind duplicates is not to avoid repetition, but to concentrate all the knowledge on a particular topic/point in a single place. If you ever had to read pages and pages of forum pages to patch together the pieces of information you could glean, you should understand why it is so much more pleasant to be presented with a single coherent answer giving all the details in an organized fashion.

Do note that even closed duplicates are not removed, they are still useful after closure as they provide alternate wording pointing to the elected "main" question. This allows people searching with synonyms to still find the place where the information is.

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So, what should be done when considering two duplicates?

It depends.

When a new question pops up, closing it immediately as a duplicate is normally rather straightforward. However this is not necessarily the best decision.

What matters, ultimately, is to have the best quality question and the best quality answers as "canonical" and duplicate questions used as road signs to point there:

• it may mean closing the older question in favor of the new one, if it is much clearer and attracted better answers
• it may mean merging the answers from one into the others (something moderators can do)
• it may mean editing the "favored" question to improve it
• it may mean editing an answer to improve it
• it may mean created a brand new answer if the existing ones are found lacking

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StackExchange is first and foremost about quality and a high signal/noise ratio, authorship or age of posts matter not.