When I set up for a new lease I was told I cannot use the old plate (coming from a lease with a different maker). I assumed the plate was attached to the car and would be returned together at the lease end. To my surprise when I turned the car in this past weekend the dealers uninstall the plates and gave the pair back to me. He told me it is mine and I own it.
Depends on the state. In Florida they track insurance and plates. If you still have the plate, about 60 days later your license gets suspended. Your supposed to turn the plate in to the department of transportation.