If a question is closed because it is a duplicate, the (current) explanation says:
This question covers exactly the same ground as earlier questions on this topic; its answers may be merged with another identical question. See the FAQ.
(emph. mine).
Is this done as a rule? How? By whom?
The only way you can merge these answers (that I know of, barring diamonmod trickery) would be copy-pasta, but you'd have the choice to edit it in an existing answer, or add a new one.
What is the write-it-out meaning of that sentence? Some options I can think of are:
- It is a hint for the writers of (the good) answers that they should add/edit them to the other question or answer (and possibly delete them here). (And only them, because it is 'their' answer)
- It is a hint to any reader with edit rights to add/edit the good points of this answer into the best answer on the other question, or if none available even add 'their own' answer, possibly with a link. The original author wont get credit though..
- something with a new answer but community wiki? (not really sure)