What part will fit and what part was original are two different things.
In Kawasaki literature & KIC whenever an original part was depleted and a newer part would fit the old part was superseded in all literature and the newer part was shown. From Kaw point of view that was logical because the newer part was available to sell but the original was not.
In KIC you can look at "prior" parts to find the original part#. However, it is part# oriented and the "prior" parts listed are not necessarily the original part(s) for the model in question. For example, if you look for a clutch release for an S3 it may show the KH400 release part number because it is interchangeable (but not original). When looking at "prior" it may show a list of part#'s that include early S1 release even though the early S1 release was never used on the S3.
Parts manuals and online parts diagrams, like Partzilla, etc, are the same way (but don't necessarily show "prior"). The latest part produced that will fit is shown and that may not be the original.
A parts manual that covers several models will almost surely NOT show the original part# for an earlier model. If the listing shows the same part# twice that is a dead giveaway that the number provided is not original.
The only manuals that can be trusted for original part# application are those printed before a later model was introduced.
Ebay application information is notoriously wrong. Even if it says the part was removed from a particular model. How many times was it replaced over the past 40 years? Same is true for a guy that says "my bike has xxx". Unless he was the original owner he doesn't know... and even then memory about what he may have done fades over the years. Right now there is a painted sprocket cover listed for an H2, removed from an H2, that has no hole. In reality it is an early H1 cover, never originally used on H2.
Aftermarket suppliers are another ballgame altogether!
I have tried to use early printed manuals and authenticated info to construct the Triples Part Database:
http://www.kawatriple.com/database.htmI won't say there are no errors about original part application (especially fasteners) but it is probably the most accurate info available.