I guess you can get the portion of the year you will not use it. If you have to pay 120 dollars for the year the number of your due date is 6 you should get 60 dollars back.
When I changed my plate in 2000 year, I sent qc a notice of the driver license and plate change ( but I did not returned the plate and they did not ask either) I received a cheque about thirty or fourth dollars.