you could, instead of only checking for the author, also try to check for the maximum amount of patches. If you find patch [Patch 1/7], I assume you currently wait for all 7 patches. Now if a patch 1/3 comes in between, you'll see that the maximum is different, in this case 3, so you'll know that it's a different patch-set.
I thought about that, but the drawback is that a new patch set is started if the submitter mistypes the maximum (e.g. [1/4], [2/4], [3/5], [4/4]). In that case we end up with two incomplete sets.
This should be a pretty rare case given that most people will use some generators like 'git format-patch' or 'quilt' for their patch-series. I'd say if such an error ever occurs, the series could be manually fixed/resent. That way, you don't need to code some UI and the authors who have not done a mistake won't need to take an extra step.
Kind regards,
Wolfram