This question is not a personal complaint towards anyone. That's the reason I'd rather not give examples and I don't think I need to. The question is a call to be a bit more aware of what we are doing here in general, and to prevent that we create a jungle of repeated information; a call to watch over the quality of acting.
It happens to the best of us; posting an answer on a question that is a perfect duplicate of an older question. I see that as more or less unavoidable; many times questions have an unclear title, are asked much more specific then needed, and (possible) solutions fit a much wider range then the asker even understands.
(Too) many times however, obviously exact and undeniable duplicates are answered nevertheless (again), not by "greenies", but by pretty much experienced users, who should know they are duplicates. Often even after the question has been marked as a duplicate. It feels faint to repeatedly see answers appear, a considerable time after you marked a question as a (obviously perfect) duplicate.
While original questions often already have a quality answer, well elaborated and still perfectly applicable, a reformatted copy of the accepted (original) answer is posted nevertheless.
Again, I am not judging anyone, but I really think we should not be so eager that we post (again) answers that we know have been given in the past. Many times even after the post has been marked as a dupe, accompanied by a link that offers the best answers on the site.