I think you should have bumped one of the other "there's been a lot of bumped threads" threads!
Seriously though, I don't see any need for a hard and fast rule. If the content of a thread is still prescient and any important links are still live, I don't have a problem with threads being bumped. At the same time, we can't expect everyone to have a black-belt in Google-fu, and the search facility here isn't exactly the best. I think that quite a few are accidental anyway; I know I've done it myself. I sometimes forget that I reached a thread through the suggestions or a search, and I use "posts since last visit" most of the time, so I forget to check posting dates. When there are little flurries of it, it might just be new members learning the ropes.
I don't see why a polite "hey, have you realised" should be a problem if someone seems to be replying to nobody, nor if they respond that they're aware of that but the thread's still relevant to them.
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