I don’t think there are technically dupes. You could have multiple communities across different instances all called “gaming”. But that wouldn’t mean they all share the same rules and posting formats, etc.
They’d basically be like different subreddits. So you could potentially create a multireddit, but not truly merging “duplicate” communities.
Ohhh, yeah, that is a sort of unique issue. Even then each one would have different vote and boost counts as well as unique comments sections. I think with a clever enough UI you could still work it out, though.