Grizzly Part Numbers Confusion

I’m still working on a 1998 Yamaha Grizzly YFM600FWAK. Why do there seem to be some many different part numbers for same thing? Looking for cam chain:
1. Yamaha gives 94590-27126 Yamaha Motor Canada
2. Motosport OEM gives 94591-40126-00 OEM Yamaha Utility ATV Parts | MotoSport
3. HLSM OEM part finder gives 94591-45126-00

Rules state, cannot post actual links, so the sources are provided.

All these are supposedly for the Grizzly 600 as above. Can anyone explain what is all means and why the different numbers? Possible the numbers change up, but cannot find any information to verify that.
More confusing are the cam chains on Ebay, because many provide the year/model number for compatibility but no part numbers.