Jake,
take the AW11 MR2:
Later (87-89) rear brakes are larger, and bolt to the earlier suspension, but the later suspension doesn't bolt onto the earlier tubs due to revised rear engine room stampings and the associated changes to bolt locations. there were a lot of other changes along the line in these cars: bumper contours, tail lights, radiator mounting plane, front brake diameter and thickness, the position of the parking brake handle and many dashboard details, the rear wing came in 3 different types (2 pice, no light, with light in middle support, and with LED in the wing) OR without the thing, the transmission was upgraded to a new PN, pistons, rods, and crank (just rod journal diam), computer, AFM, wiring harness routing, air filter location, evap system, added a drain plug to the gas tank,... hell they changed the orientation of the letters on the valve cover.
but it's all a MkI MR2. they all share a chassis code, an engine (though different generations), and a spec line, and to an uneducated observer are all but identical.
if I swap later brakes onto 85 car, I just made a combination of entities that never existed, by updating along the specline. legal?
if I swap the LED wing onto an 88 car, I just duplicated what is identical, otherwise, to an 89. I just updated an 88 to an 89 but did NOT make a combination that differs (aside from the VIN) from a car sold through a showroom. legal? (obviously)
what's right? and more importantly, why? the less obvious mid-model run changes are what can create "unique" cars. upgraded factory bolt ons are obviously under the intent of the rule, and if nothing else changes there's nothing else to say. but something else always does. so the rule is, under the strictest reading, rendered NEARLY useless.