90+ models have a 2-piece clutch cover among a bunch of other internal changes. This isn't an issue in itself, but I believe you cannot fit an 89 clutch cover to a later motor, so any 90+ motor stands out.
That said, the changes aren't huge, so you could probably make an argument that they are an eligible carry-over part.
Forks changed every year, and changed significantly in 91 or 92. Easily spotted by the steps in the upper tube between the triples.
Aussie delivered 94 & 95 RMXes got the upspec jap model, based on the 93-95 RM. These are easily identified by the radiator shrouds that cover the fuel tank. They are definitely not carry over bikes.
The yanks only ever got the same basic bike from 1989 to 96. The 96 got right way up forks.
Australia got the old/yank spec bike in 1996.
The last two points confused the hell out of me until I figured it out.