I think in HN terms "dupe" means this story was on front page for some time and got some discussion, just a previous submission with few upvotes and no comments

I think in HN terms "dupe" means this story was on front page for some time and got some discussion, just a previous submission with few upvotes and no comments doesn't count as a dupe if it's clear it hardly can get on front page now (older than n hours).