The two important things are that duplicates are ok after about a year and most other duplicates get caught by users and moderators if they get past simpler checks. So fundamentally the technical problem of dupe detection is not all that important to the site. There's some annoyance for submitters who feel they miss out on their rightful karma when their submission of something doesn't get traction but I guess they are a small magnanimous fraction of all users.

The main thing to know is that reposts are fine after a year or so. pvg has already pointed this out but it's worth emphasizing.

When I post "related" links like in https://news.ycombinator.com/item?id=32135274, the purpose is simply to point readers to other discussions they may find interesting. It's not meant to imply "these are dupes that shouldn't have been reposted". I hope that's clear!