There is no reason to register a bike intended for racing. It could well be that it was bought or sponsored brand new as a race bike raced for 2 seasons then registered for road use

I've got 3 600s none of them has ever been registered one of them is a 1996 model. I could in theroy get a certificate of newness from Honda and register it now.............. mind you it would'nt be exactly legal to ride it on the road I'd need all the road parts to do that.