The after market manuals are not published for one year. The publishers are trying to sell as many of any one book as they can so these manuals will have a lot of stuff you don't need and some stuff you do need won't be in them.
I just picked up my Clymers manual, off the floor, and notice it is only a three digit issue, M502. Maybe there are others? Mine is a second edition, 5th printing, September, 1999. It is the black cover with a Silver R90/6 on the cover. It says it covers model years 1970-1994. I guess that's enough. Mine does not say what models with in those years but I didn't look very far into it.
You might have an issue with a manual that doesn't cover some of the specific gear on an R100R. Aren't those just a couple of years and they have Para Lever drive shafts or some other weirdness?
Mine does have Para Lever drive shafts.
Things like carburetors. The manuals don't show you an explode diagram of every different model. Just in CVs there are three different tops and two different ways of attaching jet needles. And forget finding diagrams of early /5 enrichners.
I have the Clymers, Haynes and BMW Shop Manuals. I also have an older Clymers, with the red /7 on the cover. The old one says it is edition M309. Published in '83. It goes up to 1982 models.
Do the best you can selecting one, get at least one manual, Clymers is a good choice, but no manual will cover everything.