Maybe I am dense this morning.

Without studying the schematic, the text of the OP states in multiple places that power is cut to the score relays. It also states that the score relays can still be energized.

Just as a cold reader, the language does not make sense to me. To say that there is no power to the score relays and then that the score relays can still be energized isn't clear. Maybe I missed the point???

I am dense. I still cannot see the potential issue. Please correct me if my thinking is faulty.

If the NC blades of the M/B switch on the tilt relay (shown within the red circle) were to "malfunction" and cease to conduct, while the NC switch that Howard points out was still active, the schematic appears to show that malfunctioning (non-conducting) leg of the M/B switch also prevents all of the NO score relay switches from having a path to ground.

Thus, even if any of the various score relays happened to get energized, the NO score relay switch does not have a complete circuit and should not have any way to send a pulse to any of the (unpowered) drum units.

I have to agree with Howard that I've never heard of such a problem occurring with multi-player Williams EMs.

Maybe I just need a Red Bull in place or more coffee?