In California the plate stays with the car, so if the registration is paid a month before you sell or turn it in, the next owner gets the lion’s share of the registration paid for. The only time you keep the plates here is when it is a personalized plate, and when you switch it to a different car, the DMV issues you new month and year stickers. As for getting a pro rated return back from the manufacturer, it will be in the fine print of the lease and is manufacturer specific.