If you rebuild a car into a factory supplied, brand new shell, then it remains as the same vehicle.
Fair point but that does imply actually using some parts of the original car, other than the number plates. Don't they have a points system these days? So many points for the original engine, axle, shell, suspension etc and you need a certain amount of points to be able to retain the plates?
I don't see anything there that dates back earlier than 1974 except for the roof. Which dates back to 1968/9.