Google for like situations. Was the car sold or retitled?
Can you prove it? Can you prove the car was re-registered and reinsured promptly? The state should have this in their database.

I've moved away and not sent back plates. (Long ago though.)

Traffic ticket lawyers cost about $300-$400. If you need a lawyer, one of those might possibly be able to dispute this and save you some $$$.

I just received a letter from the MVA regarding the registration on my mom’s vehicle. My mom died in late Aug. Her insurance carrier canceled her policy shortly thereafter.

I’m trying to confirm whether or not the estate is going to be charged $900+ in fines for turning the tags months after insurance was canceled, due to my incompetence.

I was appointed as executor in January.

Thank you.