From others comments on this very question it's clear there's no conventional or consensus agreement among forum users on what should be done about in such case. It therefore suggest that you can use your discretion knowing when you're bumping or spamming on a particular thread that has already been discussion. And things that anyone should consider to knowing if you're spamming or should bump on an already existing thread is; the duration of such thread; when last was it edited or a comment was made in the thread was it 2 or 3 years ago; or are the answers to the question of the thread now obsolete and you have current updates to it which could be so elaborate.