Can multiple mailings have deduplicated email addresses, so each address will not receive multiple emails?
Hopefully someone else comes by with a simple strategy - here is an off the cuff idea.

a/ you know the emails you sent to
b/ if you import emails then you can add them to a Group
c/ i don't know if when you import an email that is used by several folk they all get updated, it may only update the lowest cid
d/ if the import does do what you want then you can probably figure that path from there