Yeah, I had one ride around behind the seat of my truck for >10 years. I eventually turned it in and was told it was so old they no longer had record of it.Another fun fact. One is SUPPOSED to mail in the tag for the plates of a car you sold if you don't transfer it to another car or if you decide not to re-register an existing car.
In theory one of the HP folks will come give you the knock if you don't. Experience would indicate that must be pretty far down their priority list.