OK, I think I may have this mechanism... better understood. Or, at least can offer a good guess.
First, some cautious verbiage from ad and manual writers at Shimano describing the “Lure Control” feature, which differs from the “Cast Control” feature. They say "feature" but don't describe the mechanism or how it works. Which leaves those questions -our curiosity- hanging. I guess that's the point. I believe that true BFS really didn't take off when the EX appeared, and took some time even after magnetics appeared. So, I wonder about its efficacy, for the average caster.
The Cast Control is an ABU like centrifugal brake. Both the 100 and 100EX have them. The 100 has a standard looking C-brake on the tail-side spool end. The 100EX has a smaller version on the face-side spool end, probably to minimize braking for light casting weights. See schematics. Interestingly, perhaps, is that the schematics do not show any detail of the Lure Control mech. Replacement parts must have been integral with the frame?
The spools on these reels also appear to have a Shakespeare Wondereel-like central weight on the tail-side spool end (?). This does work (quite well) to tame backlashing on the Wondereels I’ve tried. I assume this acts as a centrifugal counterweight?
The “Lure Control” mechanism? It does appear to be a pair of gears engaged/disengaged to the tail-side spool end by a switch via an armature, stair-stepped to accommodate the ergonomic “palming plate" -new lingo then for the tail-plate.
I’m going to venture a guess that these gears simply add light friction to the spool end, as John surmised. Can’t imagine one could throw 1/16oz very far? Guessing it was a “fast” reel (there are 2 ball-bearings on either end of the spool) and that likely required some serious thumb practice. The instructions mention: “If you can’t reach the target, loosen the cast control. Practice will now make perfect.” Possibly, the combination of: ball-bearing supported spool, a small C-brake, central counterweight, "Lure Control" gears (and thumb?), (and an over-filled spool?), aid in casting very light weights? Not to mention the relatively new disengaged LW mech (a la Lew Childre) and spool/frame design present on those Bantams. Lovely reels they are. (I've been a fan since I first bought a Mag version new in 1984. Still using it today).
Like the OP, I didn’t find any commentary on how well the EX actually throws 1/16oz weights (does 35ft count?), although there have been a few people asking. I’m guessing such talk would be in Japanese nowadays. Perhaps Ron Mc, our resident BFS expert, knows something about these?
A manual for the 100 and 100EX, which describes “features” and the C-brake Cast Control, but not the Lure Control.
https://www.planetseafishing.com/wp-con ... manual.pdf
There is also a YouTube video of a 100EX being serviced. it reveals the mech but offered nothing on how, or how well, it works.
Not sure how much this helps. But it does settle my curiosity a bit. The year after (or thereabouts) the EX was discontinued (1982 I've read), magnetics appeared and apparently Shimano and others never looked back.