You register for the decade your car debuted in. For example, BMW E30's came out in the 80's, but continued production into the 90's. You would register in the 80's class. MKV's the 00's class and etc... This will create a cultural commonality in the class competition, and keep old school from competing with brand new cars, creating a competition structure that is fair, unique, and competitive while still embracing the European car cultures.