As an example, this 2011 question:
was marked as duplicate of this 2009 one:
However, in my opinion (admittedly biased, as I wrote the answer to #1), the later question had a MUCH better set of answers (the second question's main accepted answer is actually somewhat wrong, as per the highly voted comment under it. It has 1 good answer with 7 upvotes, and another which would have been good except it's merely a link with no content).
Is there any reason why the first question was closed as a dupe and not the second, given the relative answer quality? Was it merely the date of posting?