You run in to the same thing with cars, motorcycles, outboards, and may other things. The problem is that some parts are used over multiple models for maybe 20 years, while other parts might have only been shared between models for 5 years or only with a portion of that same group for 7 years. And as far as I know, there is no manual that groups them together based on shared parts. You just have to pick a specific part number, then look at a parts cross reference to see what models shared that particular part. Of course this sort of information isn't very useful until you start looking to source replacement parts from salvaged motors because that part is no longer manufactured new.