Jim, Certainly could have been trapped air. I think it unlikely however I wouldn’t discount anything at this point.
I experienced air trapped in my car several years ago after a MC failed. I had a devil of a time chasing all of the air out of the system. But that situation was different. I could get a spongy pedal, just not real solid one. Careful vacuum bleeding cured the problem.
This was different. We had no pedal; none to speak of. She went clear to the floor with no resistance. The kind of pedal that makes one think there is a growing puddle of brake fluid on the ground somewhere every time the pedal is pumped. And nothing we did until changing the distribution block had any effect whatsoever.
Maybe if I get a chance this weekend I can inspect the block we removed as I would like to determine a cause. I've personally never had an issue with either a distribution block or a switch thus I've never had cause or opportunity to fool with one.
