The only way to try to make any sense of OS designations is to got to the timeline at http://www.osengines.com/history/ostimeline01.html and work your way through. This isn't an official OS site because it's done by the American importers and there are a few inaccuracies and isn't totally complete but it's by far the best around.

If you follow it through you'll see the 35FP was first made in 1984 but you'll see it listed again in 1998 when they changed it to a remote needle valve so it had quite a long run. Strangely enough this is where one of the errors is because the '98 photo is supposed to be the CL version (FP-S) but it's got the RC carb. I can't find any 35FS though.

As far as the suffixes go, if it says 40 LA then it's the standard RC version. If it says 40 LA-S then it's CL, -M for marine, -H for helicopter. There are a couple of weird suffixes though like -B so it's up to your imagination as to what they meant by it