Duplicates are generally accepted when there was no significant discussion on the original submission.
I seem to remember there's a system in place to prevent duplicates (where the submission of a duplicate link results in the upvote of the original story), but maybe that's limited to the first 24h? Idk, HN works in mysterious ways
This has negative impact on searching older discussions. Instead of 1 result for 1 URL (within few month) getting 2 or even more.
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