Does the atv industry have an industry standard as to build dates and year models.

I know in the auto industry when looking for parts anything with a build date of the 9th month is considered the next next year model.
is an 87, but the build date is 5/86.
The 86 parts rig I picked up yesterday is an 86, with a build date of 3/85.
If I am not mistaken, I have read on here that there is some differences between the 86 and 87, mostly electrical iirc, but wondering if my 87 was built ai may of 86 if the parts would be the same as the 86?