If it's the same basic story, we treat it as a dupe. We might not mark it explicitly with the [dupe] marker though.

Dupes have more to do with how close they are to each other. The same article posted months apart isn't a dupe, different articles on the same subject posted hours apart is a dupe.

It's not automatic, but sometimes the mods decide manually to mark it as a dupe when the new one has no additional information and the other had a big discussion.