The HN policy seems to be that later posts on the same topic (even if they're different urls) will be considered duplicates, unless an article adds significant new information [1]. Otherwise you get discussion about the same topic split over multiple threads, leading to both repetition and incompleteness on each thread.
If you think this article contains significant new information, or that it is a better source than the earlier post and should be the one linked from that thread, you should email the mods – hn@ycombinator.com.
