Bill,
What was the question? The "A1" and "LG" leads are basically grounds. In some systems, they are tied together at the equipment box and only the "A1" and "LG" leads for the first line is brought to the telset. The second through last line buttons shared the ground leads from the first line.
Now, there were some systems that needed the "LG" leads to be separate from the telset to the equipment. This was when the lamp was to "wink" rather than "flash". (Usually a phone being called from another station on a two-path intercom unit (6A?). Then the ground to the lamp would be opened briefly to effect the "wink". Thus, the "LG" leads had to be unique to each lamp.
bob
***** Moderator's Note *****The question was: did only N.E.T. use the "LG" leads as the "HOT" lead for the lamp? I tried to wire a 660 com panel to a KTU, but I assumed that the LG leads were Lamp Ground, and tied them all together. It didn't work, and then I was told "LG" meant "Lamp Gain", i.e., that the LG leads were the power feed for each lamp, and the "L" leads were the ground.
I think you've answered it: only N.E.T. had it backwards. I still wonder, though, if it was a Boston-area fluke, or if the practice was common throughout New England.
Bill