On HN we don't count a post as a dupe if it didn't get significant attention. (This is in the FAQ: https://news.ycombinator.com/newsfaq.html.) The dupe detector is left porous to allow good submissions to have multiple chances. It's one way to mitigate the randomness of /newest.

Of course this also allows bad submissions to have multiple chances, but it's more important to facilitate the good than punish the bad.