The important date is the postal date on the outside envelope.
Honestly the state should mail a card to every mail in voter that the ballot was recieved, on a specific date, so that they know the post office did its job.
Can the postal date on the outside of the envelope be falsified?
Are the envelopes and the ballots separated during the counting process? Is it possible that some ballots with late envelopes are counted, if there is no date on the ballot?