I reviewed your latest continuity and DC power results and drew up the above diagram. Here's another one for you. Add "suspension of disbelief" to what we have here.
So now it appears the wiring of the 2002 versions (your #2 and #3) are indeed different. So now my previous hypothesis that you could see which 153IR version you had by simply looking at the left power terminal markings (U-A or A-U or unmarked) was WRONG. You have to use a meter (continuity testing) to see what you have. That's what I mean by suspension of disbelief. Yikes!
BUT, with your specific combination of 3 153IR's, this may be one of those blue-moon events where the stars are in alignment...when 2 wrongs make a right...and two Wrights make an airplane.
Thanks to your methodical approach to the continuity and clicking measurements, I believe this can still work with DC powering all 3 153IR units. I will next work on an exact diagram including broken #2 unit terminal. Just wanted to assure you I'm still on-the-job!