Factory body parts for certain ingame cars

It is well known that certain cars have different looks in some domestic markets, the prime example being Honda Integra Type R DC2/Acura Integra Type R. Instead of adding a whole another car in the game, wouldnt it be easier to just add body parts from other regions? I mean, I’m the expert when it comes to licensing and such, but it sure would seem much easier to add a set of body parts instead of a whole car. Especially if the car was already previously featured in the Forza franchise. The same principle can be applied to the american muscle cars, due to having a lot of different versions released in a short time, some body part options are left out because of the car choices for Forza games.

The cars in question are:
Acura Integra Type R (Honda Integra Type R DC2 body parts)
Acura RSX-S (Honda Integra Type R DC5 body parts)
1970 Chevrolet Chevelle (1971 Chevelle body parts)
1969 Chevrolet Camaro SS (1967 Camaro body parts)
1970 Chevrolet Camaro Z28 (1970 Camaro RS body parts)
1970 Dodge Challenger R/T (1971 Challenger body parts)
1969 Dodge Charger R/T (1967 and 1970 Charger body parts)
1969 Ford Mustang Boss 302 (1970 Mustang Boss 302 body parts)
1993 and 2000 Ford SVT Cobra R (non Cobra factory body parts)
2006 Hummer H1 Alpha (Army Humvee bodykit)
1994 Mazda RX-7 (Type R, Type RS, Type RSR, Type RZ, Bathurst R body parts)
1971 Plymouth Barracuda 426 HEMI (1970 AAR and HEMI Cuda body parts)
1992 Toyota Supra 2.0 GT (3.0GT Turbo A and 2.5 Twin Turbo R)
1985 Toyota Sprinter Trueno GT Apex (Corolla Levin and Notchback body parts)
1983 VW Golf GTI (non GTI factory options, Rabbit body parts)
1992 VW Golf Gti 16v Mk2 (non Gti factory options, Rallye and Country body parts)
1982 VW Pickup LX (EU spec body parts)
1963 VW Beetle (other factory options)

The images of all the mentioned cars will be included below:











hmmwv-humvee-04

1970-Plymouth-AAR-Cuda-1











EDIT: I replaced some pictures that looked bad.