You can run any COMPLETE gear set that came from the factory (for sale in the USA) in the classification, configuration, production years, & model of the car you're racing. If you can't pretty easily prove that this was the case, then you're dancing on the line of legality and at the mercy of whatever tech shed you're standing in at any given moment.
For example, the spec line for my FP Integra specifically says "90-93 Acura Integra", with no specific model designation given, other than limiting to only those with the "81.0 x 89.0, 1835cc, 4-cylinder engine". That effectively limits it to the RS, LS, & GS models. Gear wise, those three models were always identical, however their gearsets changed between 90-91 and 92-93. So in my opinion, I could run a complete 90-91 1.8L gearset or a complete 92-93 1.8L gearset, without any penatly. Additionally though, the 1.7L GSR model also existed during the 92-93 years, which came with a really nice close-ratio gearset, but that could not be run without the 2.5% weight penalty in my car because it never came stock in a 90-93 1835cc Integra.
I know in the land of Honda's, it's REAL easy to piece together a pretty slick transmission using nothing more than cheap and readily available OEM gears from various Honda/Acura models and trim levels. I'm sure that's probably the case in VW-land too. But if what you're trying to run didn't come as a complete gearset in the classification, make, model, and trim level of the car you're trying to race, and you can't pretty easily prove that it did, then at the very least, you're in a place that I wouldn't chose to be. The transmission in my car contains nothing but OEM Honda gears, but they're not one of the two complete OEM-sets that the car was ever delivered with from the factory, so I take the 2.5% penalty.