Ok, I think I need help on what address lines to examine for the next step.
The following chart may be hard to read, but I'll try to explain it... While not quite yet an actual circuit diagram, I wanted to map out where all the 24x4 = 96 pins of the Display card when to, on the Display card. So yep, using the DMM and tinfoil, I started exploring. Many were obvious traces, but I did end up needing that tinfoil to help isolate down the area of quite a few connections that didn't go just straight up/down or across the board.
The Display card has two main groups of components: "tincans" (the silver square IBM chips), and 14-pin or 16-pin IC's. (then a few resistors, diode, and whatever those "915" chips are called - a capacitor of some type).
Anyhow, I'm concentrating on IC's and "tincans" and I labeled them like this (1-7 on the tincans, 1-15 on the IC DIPs). The set of 96 pins at the bottom of the board connect (and are exposed from) the A1 board, so I'll call those "A1-pins" or "external pins" (from the perspective of this Display card). It turns out that tincan 2 and 7 aren't referenced at all from any of those 96 pins, so they are for "internal processing only" (likewise with several of the DIPs). I didn't concentrate yet on the internal interconnections between these chips, just on there the A1-pins go. (the numbers are "backwards" in the image below, because I was working from the perspective of the solder pads on the backside of the board, so I was never really even looking at the component side)
So, here's the tentative result.... On the left in each box is the DB GJ MP SU from pins at the bottom of the Display card, then I just tested continuity to find the "first major component" that these pins had continuity with; most of them had several intermediate pad connections along the way to that first-component; I do have another diagram that marks those, but the following was the most concise way I could come up with. On the right side of the boxes below: the IC chips are standard pin number arrangement, but for the tincans I just numbered them in-sequence from top to bottom of the pins they had. It doesn't especially matter which pin on those, since we don't know inputs vs outputs on those chips anyway.
"Rx" is that the pin connects to a resistor in parallel, not that the signal goes through a resistor.
"951" is code for these little "monolith" components marked with "9" in white background and "51" in black background, which I think are a small regulating capacitor.
I wasn't sure the best way to group these resulting notes, but I grouped by them by major IC chip (tincan or DIP).
There are some pins that are truly NC ("not connected") and I removed those from this diagram. But there are a few that per the SLM that were "not connected" and yet seem to still have a connection (these are marked in black background).
So my question is: to find this "stuck address pin", should I be looking at "SA" pins? But those are outputs from the Display card (Storage Address Bits).
What are the Even/Odd bits? Those are inputs that go to the Display Data Register. I assume its related to the characters on a row being in some Even/Odd column assignment? Or maybe it relates to being in REGISTERS mode, and showing portions of bytes vertically in Even/Odd Rows? Or something else entirely.
Or should I be focusing on the BO (BusOut) pins? Notice that two of these go straight to an IC (#12) instead of the tincan5 like the rest of the lines.