I'm specifically thinking about this question, but it's true in general. StackOverflow in general is well known to be extremely aggressive in closing questions as duplicates without much justification, and the things suggested in the help article only do anything within a few days of the question being asked; after that you're SOL if you wanted to get an answer more informative than the accepted answer for the ostensibly-duplicated question. (In the case of my question, I had already read the answers there before asking my own question, and they did not address my problem. But good luck convincing a drive-by deletionist of that.)
What policies exist to deal with this kind of problem?