What do you want to know?
You can always look at the patents -- which seem to have expired, by the way:
https://patents.google.com/patent/US4910888A/en
https://patents.google.com/patent/US4575957
(Caveat -- I'm not one of those guys who has model numbers etched in his brain. I may need to go in the basement and check some details, and may have the model numbers vs evolution slightly skewed.)
The 90 and 91 were pretty much the same. The heel lever was improved (wider, less prone to cracking, maybe less prone to ice build-up in the socket where the clamp lever pivots). The cable material seems to be more rust resistant, or maybe I just dry my boots better. My original SX-90 had the internal cable break (in the middle of STH at Snowbird!) about the 2nd year of use.
With the SX-92 they combined the function of the heel-hold down cable lever and the calf-closure buckle -- one lever for two cables. In my opinion, this was a big step backwards. But the "92E" version kept the two functions separate. (The fore-foot width adjustment seems to be unchanged throughout.)
The last version, variously named the SX-93 (maybe 93E) and the "Force 9" kept the separate closure mechanisms and added a top velcro strap, a bit like a booster strap,
https://patents.google.com/patent/EP0492116A1/en
A few other notes:
There is a hard plastic spreader over the instep between the cable and the liner.
The SX line followed a machinery paradigm instead of a shoe-maker's paradigm. For example, there are two spots the hinge on the upper can screw into the lower, changing the forward lean. Underneath the bootboard, there are several sockets to accept plastic buttons to change angle of the board in the shell. There are small inserts that can attach inside the shell to tighten the heel grip around the achilles. The toe and heel lugs were available with different cant angles -- just replace them, no planeing or such-what.
Of course, the used ones only come with whatever fit aids the original owner needed. I imagine there were big boxes of them thrown out by a lot of shops at some point.