no it doesnt, the bikes were basically unchanged from 87 until now. there were only a few minor changes after 94, but most of the stuff stayed the same.
as for the year, its kind of like cars... the new MODEL year comes out in the fall... for example, this fall, you will be able to buy a 2008 car, even though its still 2007.
look at your vin:
1991: JKAEXVA1-MA048001 and on
1992: JAKEXVA1-NA060001 and on
the 10th digit is the year. M = 91, N=92 etc
the - in the spot of the 9th digit, is because thats a check digit, and it will change based on the other numbers/letters in the VIN