Good.
What failed for reason?
It is easy to consider that a candidate, being behind by a few thousand votes late on election night, could just flood the mail in collection boxes with phony ballots without dates, and do so to make sure whatever gaps in that candidate’s votes could then exceed the number they’re losing by.
In other words, by having a proper date, you are verifying no cheating went on. By the opposite, allowing undated ballots just makes everyone believe the election was not fair.
What they need is a verfied date of when the ballot was received.