Below are AE 80 (Desk) & 90 (Wall) Telephone Wiring Diagrams (only) for models with N, NB, NC & ND at the beginning of the code on the base.
N has a Potted Network (not a printed wiring card but a large plastic goo filled network) and they are Manually Compensated (rotary dial in base to adjust for distance from the CO)
NB can be a Potted Network like the "N" or a WA1120A printed wiring card Network and it has Automatic Compensation (no rotary dial in the base).
NC has the newer WA1154A printed wiring card Network.
ND appears to have identical components and wiring to the NC Series
Terry