I would say no. The old posts are still helpful, searchable questions (by which I mean: if you're only concerned about X/Y, then you might not open a question that doesn't say X/Y in the title). A good thing to do would be to update the older questions with any new or improved information that was unearthed by the newer thread.
In general, I believe it's a bad practice to close questions just because their answer already exists on a different (albeit related) question. "Broad" questions that cover all cases and "specific" questions that cover particular cases should be allowed to coexist and serve their separate niches. There are times where this approach becomes annoying but we shouldn't be making broad rules to suit very exceptional situations.
