I don't know when it was posted, but it definitely was less than one year ago. My main data point is that it still is living in an open tab in Chrome. I have a couple of sites which allow submitting links. I know people can get around my requirement that they are unique pretty easily. I'm sure HN is more sophisticated but I think that just having different url parameters might qualify as a different link? Sometimes a url parameter change really does point to a different page, so it might not be possible to eliminate duplicates that have the same url with just different params.