If they manage to produce what they were required by law to retain, and they come close to equaling the number of ballots cast, you then say "Now, let's give these envelopes a cursory review to check to see if they all have a signature, and have either a postmark or have a timestamp of when they were received." If you don't find significant errors at that point, fine.
If you do have significant errors, HOLD THE CLERKS ACCOUNTABLE WITH FINES AND/OR JAIL TIME.
The only way to get these elections somewhat cleaned up is to provide meaningful consequences for violating the election laws.
Having them dragged out of bed into the night by a pack of hyenas and then find their half eaten bodies the next day works for me, like that hyena thread.