I have 3 known years of OEM plastic & have noted some differences between them that seem to make them year specific. One main obvious difference is 88 has red plastic so I'm not going over that one. I only have 86's & no other year frames to make comparisons but I'm pretty sure the 87-89 frames are slightly shorter than 86 frames. The 87-89 fuel tanks are also shorter than 86 fuel tanks but both the front & rear fenders are the same length on all 4 years. Here's some pics of the differences I've found so far that can be used to identify specific years. The 86 tank on the left, 89 tank on right:
The 86 tanks have 2 round rubber protectors on each side, 87 tanks have one & the 88-89 tanks have none:
The 89 front fenders have a guide ridge on the inside that the rubber tank protector strips butt up against but the 86-87 plastic does not have this since the rubber strip is mounted to the tanks:
The 88-89 fronts also have a notch in the center of the hood mount channel where the retaining tab from the hood slides in, 86-87 front plastic does not have this since the 86-87 hoods have screws in that location instead of tabs:
Only OEM front plastic has the open slots in the scallops on the sides as far as I know:
For the rears the 86-87 plastic is easy to identify because it has no holes for the front seat mounts & the 89's do:
Also the 86-87 plastic has molded in tire info on the left side while 89 uses a sticker:
The 86-87 & 88-89 hood differences are obvious however I have OEM smooth hoods that have a part number & other info molded into them & some with no markings anywhere so I'm not sure if the hoods with no markings were originally from actual quads & the ones with numbers molded in were purchased as replacements from the dealer or if Honda started adding these numbers in 87 regardless if it was on a quad or bought as a replacement. I got my 86 in 88 & know for sure it has the factory original hood & it has no marks anywhere but than I have an OEM 88 hood & it has a part number molded into it. This hood was in a parts lot so I don't know where it came from but it has numbers:
This painted hood was original to my 86 & it has no marks:
If anyone has any other information about the differences in plastic please post what you have found.