That's from 1405 days ago. Duplicates can be submitted in a significantly shorter time-span, IIRC.

That was three years ago. The page has plenty of new information. Perhaps there should be a statute of limitations on the dupe check.

There is. It isn't an official policy, but dupe check only compares to values in some cache somewhere. Duplicate articles are FINE on HN, given that after a time period the ability to comment is removed from an article (unless of course, the suggestion is that there is nothing valuable to discuss about something n days after a conversation starts, ever).

They could add a check for identically rendered topic titles (including site name in parentheses) to avoid some of these.

That won't work for pure javascript sites like Twitter.

That title is supplied by the submitting user according to some informal recommendations. Every so often, there will be an argument over whether the submitted title is appropriate for the content. HN doesn't scrape anything for it.