Yeah I don't think there's much you can do really except remove the Medical label from them all and re-run your automatic Medical filter(s). As noted the manual ones will not be fixed though.

Do you have an offline (i.e. one that hasn't synced) copy via IMAP on Outlook or similar? If you keep it offline you at least have a copy of the manual ones that you might be able to export out and copy back in and then try and deduplicate. Not trivial and still no perfect most likely.