i don't think it's as critical as orderering parts for cars, where the VIN Number is critical if you want to get the right part.
I'm only new to the scene as well, but it appears that a monster is a monster from 93 to 96 or 97, there carburetted & parts are the same.
the later models ie & S4R ect probably have different parts than the older M900's, maybe someone with more knowledge on the subject could advise.
but for me 95 900M, finding parts & accessories is very easy as there all the same.
This is a fantastic site & i'm sure if you track back through the threads, mainly in the accessorie section you'll soon fill your favourites folders with a vast number of companies that offer Duc parts.
Also check the Sponsors section on the home page there are some great guys that support this site & have their own businesses in bikes ect. that are only too happy to help with advise & stuff too.
It's been a wealth of knowledge to me.