The perfectly written FAQ How should duplicate questions be handled? doesn't describe the case if you have 2 old questions, which one should be considered as original and which as duplicate.
I previously expected that it should be a simple formal approach - older question is an original and newer question is a duplicate.
However, there is another approach that more concerned about the quality of content.
duplicating a dead/badly asked question ...
In this case, the original question should be the one closed for duplicate, and point to this new one. Because we can't let someone "ruin" a problem and prevent others, more motivated, to find a solution.
Another clarification from Anna Lear♦ May 5 at 6:04
The date on the question matters far less than the answers.
However question Data Explorer needs the ability to comment on queries was closed as duplicate even it has a reasonable answer from Sam Saffron, but the original question Notify/contact SEDE user of fix to query doesn't have any answers, only comments.
Does Stack Exchange has a recommended policy how to choose which of 2 similar questions should be closed as duplicate?