This can turn into an ugly and very expensive can of worms.
The best advice is to go to the DMV with the Vin number and see if it's in the DMV computer.
If the Vin number is completely absent from the DMV computer then you can probably be successful in getting it registered.
You'll have to go through the VIN verification and turn signal, brake light, horn inspection processes but it's doable.
If it is in the DMV computer, and the registration is past due. You are screwed. Your only option at that point is to pay the past to registration and all the penalties.
That can be many hundreds of dollars.
This is actually pretty funny as I went through this with an old XT several years ago.
Turned out the one I bought was five years late in registration fees.
My solution to it was to register it in Ohio in my dad's name and at my dad's address.
My dad had recently moved to Ohio so it worked.
Then about six months later registered it back in California.
Ohio didn't care about the past due registration fees in California.
And once the Ohio registration was complete, California no longer cared about any past-due registration in California.