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Ok, it's like you get the comment in the replies tab upgraded (as last edited) and in the first place, right?

That is correct, this may help if you'd like them to view your comment again. However, if it does not produce a notification they won't notice it if they don't check their Replies tab manually.

Yes, this may be heplfull when you have posts with a lot of replies and yours just slipped away

It could be.