Bump. (Sticky request)
And is there a list somewhere of cars which are truly rare (not available at all in the 70 car lots for some games, i.e. only available in the lots of some cars--probably always Tradeable)? Of course, if there are no such cars, the problem will be to determine that and then clearly indicate that somewhere.
And do some models have multiple numbers. E.g. the special single-colour tradeable Skylines? The "downloadable white Corvette" (which I've not investigated (yet?)).
The car numbers you can see in the game are manufacturer based. So on each game one can determine the number of models for each manufacturer. Once people have collected all available cars in their game, they'll see if any holes still remain. (Hopefully all games, at least in each region, have same size "collection list" for each manufacturer).