I learned that my 1990 VW Jetta is a MK-II, from seeing a listing on one of the Jetta or VW forums on the internet. Nothing in the car's literature said that, the big thick Bentley published Service Manual doesnt say it. I -think- the Jetta and other similar models were MK-I's up through 1987, and became mark-III's about 1992 or so. Keep doing google searches until a chart shows up. Here is result from my brief search:
http://www.dieselgeek.com/What_gener...ave_s/1876.htm
Note that folks commonly say MK-1 or MK-I, rather than spelling out the word Mark.