If you want to get someone for failure to pay the state, go back to the person that owned it when the violation took place. I had the title with their name right on it. Why should I pay for someone else's crime?
When you buy a used car that has an expired tag, are you responsible for the back taxes due on the car when you get the new tag? I know you can bring in receipts and declare the car inoperable during the expired time and I think the penalty would be waived. I know my dad does this when he buys wrecked cars at the auction.
I would seriously think about going to court and fighting the tickets if you have supporting receipts or a mechanic declaration that the car was inoperable during the time you bought it and now. The judge may even look at the fact you were on your way to get it tagged and did so shortly thereafter. I probably wouldn't have fought it if it had been one ticket, but the fact you received two tickets for the same infraction would cause me to reconsider.