I can see why you are worried, and I share some of your concerns.
Let me clarify this: Even though I posted this in "Repair", these displays are not going back into operation. The complete system has been replaced by newer TFTs a few years ago, and the units I am working on have been decommissioned and in private storage ever since. The flaps no longer match the train lines and destinations, and I don't think anybody is still capable of performing or willing to pay for an update.
It is very likely that I am not running the circuit the way it was intended, due to the fact that I don't have any documents about how it was intended to run. That's clearly not a good thing, but there's really not much I can do about it. I'm still lacking a proper scope, which would certainly give me more insight. There's a certain chance that I will come back once I have access to one (I am actually considering buying one because my workbench is clearly lacking...) since it really bugs me.
With all that given, I'm not aiming for 100% reliability and accuracy here. The units, once rewired, will end up on display at special local exhibitions, at least some of them. Maybe some will end up in people's living rooms. They will not display any viable information, and nobody's gonna rely on them any more
The only thing I need to prevent is that one of the units will catch fire or something like that.
About the "sweet spot": I wouldn't exactly consider this a digital circuit, I'm only trying to retrofit some kind of digital control so it can be run again.
And for documentation: I'm working on that. There will be some more schematics and probably a design for an Arduino shield once I'm finished.