I noticed that messages were being send to email addresses that were supposed to be filtered.
What I have found is that if you add an Email Filter to the list, this does not affect any campaign that has already been setup.
Also, any campaign that you clone uses the email filter list that was active at the time the cloned campaign was created, not the current filter list.
I would suggest that the email filters should be dynamic and not static.
Whenever you add an email filter to the list, I would suggest that it appies to all messages sent whether in a new or existing campaign.
IF there is a use case where you would not want existing campaigns updated with the new Email Filters, there could be a “Do Not Update” check box in the campaign setting with a warning if selected that no changes to the email filters on this campaign will be made.