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The fact that on the fifth time it rose to #1 spot, while not getting more than 2 points the first 4 times it was posted shows just how much luck is involved in getting past the "New" page.

All of those were posted by different people. It is indeed common for articles to get posted multiple times, sometimes making the front page and sometimes only getting a few points.

I don't believe this claim is correct... all 5 submissions were made by different users.

How is that HN didn't de-duplicate the URL?

From what I've seen, if a story hasn't gotten significant votes or comments (and I think there's a time interval involved as well), it isn't considered a dupe.