For North American models is it generally considered to be the year/model starting with the 9th month of a specific year through the 8th month of the next year. This isn't always the case, for example, when a bike is released as an early year model, and whenever they felt like it, but it applies pretty well for you Norte Americanos.
Look at the tenth digit (from the left, or the eighth digit from the right) of your 17 digit VIN starting with 'W', if your bike was originally specified as a N.A. model, and not a grey market import, then the letter G would signify it being a year/model 1986...
1980 A
1981 B
1982 C
1983 D
1984 E
1985 F
1986 G
1987 H
1988 J
1989 K
1990 L
etc, until they ran out of letters/years and it got more complicated.
Note that they didn't use an 'I' or 'O' or 'Q' in later years because it could have looked too much like another letter or number. This won't apply to early Australian/New Zealand or grey market import models with the K100RS0123456 (for example) type of VIN.