ideally/legally the envelopes were time stamped upon arrival.
ideally/legally the ballots were kept with the envelopes
Postal Service workers backdated some.
That’s probably the real issue in NV too. They separate the mailing envelope from the ballot envelope. Can’t go back and re-check the signatures or the time stamp.
No idea what the proper remedy could be.
Why these places are not under constant supervision and video monitoring is beyond me. In the UK, and even NYC, they have video monitors everywhere. Mostly to catch crimes in progress. But for elections, every van that delivers ballots, every room that stores ballots, every desk that counts ballots should be under 24/7 video surveillance - and live streamed on the internet.