I recommend forgetting about it now. Don't poke the bear.

Here is a Reddit thread that may cheer you up. It appears the purpose of the fine is to prevent people from driving around uninsured. If you have records to prove your car never went uninsured, that's helpful. Also keep the bill of sale from you old car.

Stash any info you've got and wait for them to bother you. At this point the possible fine is so ridiculous you could go to the media and get out of it. You haven't done $41K of damage to society and if you were continuously insured it seems like you may not have owed a fine.

https://www.reddit.com/r/maryland/comments/17tuis7/im_selling_a_used_car_in_maryland_the_mva_says_im/#:~:text=Can%20they%20issue%20temp%20tags,smart%20idea%20if%20they%20can.&text=Yup%20gives%20you%2030%20days%20till%20you%20get%20inspected.&text=its%20your%20resposibility%20to%20turn,cancel%20insurance%2C%20fines%20are%20high.&text=Had%20the%20same%20problem%20a,guess%20they%20figured%20it%20out.&text=You%20just%20went%20into%20the,they'll%20unrestrict%20my%20account.

I don't know when the law went into effect but I'm thinking I may have a Chesapeake Bay heron plate from 1998 in my non-DMV garage. Long moved away...

run away to a different country

I moved to Virginia in 2009 from Maryland and realized today I still have the Maryland car tags. I registered the vehicle in VA almost immediately after the move and have been living in VA since then. I was just checking how to return the tags and found out that there is a fine of $7 per day for not returning the Maryland car tags. That is a fine of $41000! The car has been sold several years back while in Virginia.

Can anyone who has experience or knowledge of these things please suggest what I should do?

Thank you!