I believe the dupe checker on links just checks the specific link you are posting, not related topics.

For example, If someone posted an x link and you post a bitter link, it won't catch them as dupes.

Once you post, If you expand the rated posts section you will be able to see things that are on the same topic...and sometimes which may be construed as dupes.

One way to avoid dupe posting is to do a quick search before starting your new post, but that doesn't always work either. So, I figure sometimes we just end up with dupes. So your beat to add some value by explaining the link or adding some context.