I don't know, I've been there before too. Bought a car secondhand and was later told it had XXX upgrade and YYY modified by one of my racing buddies. And since the B4 and the B4.1 are pretty close I could see there being some confusion.
I have 1 or 2 cars that I haven't run in a while and 1 that I have had for over 10 years that I'd be hard pressed to tell you exactly what is in each one.