This is the first schematic I have seen where the system voltage polarity is reversed, i.e. - on C and + on A and A. Most apply +24 volts to the contacts and the master relay grounds (-) to A and B. What publication is this document from?
Here is Page 16 from the ITR Service Instructions No. 230, April 1, 1938
You would have to ask Jim where they are from. My guess is they are from a 1950s IBM or maybe even Simplex Service Manual built around the 090 movement found on the 91 series masters. That is what Jim gave me when I had questions on my 91 series master. I also think the print you are showing is from clocks that use a seperate relay to transfer between the A and B wire, rather than use the stop contact on the clock. I called it the Duplex Relay, but some masters were wired to run 3 and 2 wire systems of impulse correction and had to accomplish the polarity reversal of the two wire systems vi a reversing relay, and the stop contact on the master controlled that relays coil. My 25 master has such a set up. I do have a diagram from the same 1950s manual that shows the Duplex Relay set up, id just have to get it off a disk and upload it.