OK, I'll throw in my monkey wrench............ First, my observation on my Gen II was that the lever was not as far away when clutch disengaged, but it had to hit the handlebar or almost, to disengage the clutch. Changing to a Gen I slave meant adjusting the lever to be further away from the handlebar to get the same disengagement point at the handlebar. Longer fingers required, in other words. But, remember, nothing changed on my bike as far as the clutch basket stack or the push rod, on a then relatively new clutch. I got the Pazzo levers which helped the reach a bit.
Design-wise, the master cylinders are all the same for all years, it just took more fluid to stroke the larger Gen I slave... we all understand that. The amount of pushrod travel with all things equal would be the same amount to disengage the clutch. Mama Yama would have designed the amount of protruding rod into the slave cavity so there was extra rod to compensate for clutch wear. How much, we don't know, how much wear does it take for the slave to bottom out and not completely disengage the clutch we don't know. It should be 3 mm or more...... keep reading.
However, the big players in reducing that rod length are the friction plates as they will be the fastest wearing parts in this whole deal. If we assume a new plate is 3.10 mm and one at the wear limit is 2.80, then in the 7 plate stack we've lost 2.1 mm. of effective rod length/room for the slave to bottom out. That doesn't count any wear in the two thicker friction plates or any of the metal plates, nor any of the pressure plates. If we add a bit for the two large friction plates, let's make it 2.5 mm. (It's really more complicated than that, as not all these will wear at the same rate or amount).
What is a constant is the larger spring #12 or #13 depending on which diagram you're looking at, is compressed significantly as it is bolted on by 'pressure plate 2'. It's more than enough force to keep this stack tight so you aren't likely to get clutch slippage (unless you got the wrong oil or the friction plates are severely worn). You've got to screw those bolts in a long way to seat pressure plate 2 and it's a lot more than 2.1 mm.
In my opinion, any changes to the parts for various years in the clutch basket and the rod, etc. won't be enough to lose the required amount of protruding pushrod into the slave cavity. It's an opinion, until that's proven, but one still has to think the effective rod length at the slave cylinder has a very similar if not identical amount of margin.
James' high miler has likely worn friction plates, therefore he noticed when installing the Gen I slave he couldn't get enough stroke to completely disengage the clutch. I suspect he's run out of effective rod length to do so. Or, if by chance there is more rod/slave travel available, he has got to put the lever in the next position forward, which is likely not ergonomically comfy at all. Certainly beyond my reach to operate the bike safely.
Anyway, that's my spin...................
