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this happens all the time though...random old threads popping up again. but they aren't banned.

realistically any thread that begins to reach 30 pages or so...i would venture to say they are off topic to a certain degree.
 
By default, threads are left open. Only when a thread gets out of hand or causes too many problems is is closed. There are occasionally reasons to post in an old thread when the subject becomes relevant again. If not, it can grow dusty whether it's opened or closed.
 
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