Not sure what you mean by "still registered", but if you mean does it need current tabs as far as the State is concerned:
Dunno about your State, but in mine (Washington) current registration is only required if a vehicle is using public roads. One can let a registration lapse for years, then go in and "renew", paying just for the current year. Gonna do that if I ever put my '65 Falcon wagon back on the road...
No penalties for lapsed years, but reregistration is tied to original month/day, so one can lose a few months that way.