While waiting yesterday evening for the M104 at 42nd and 6th, I perused the posted bus maps.
The one for the M42 dates from 1987. At the time the M42 had only one branch; it ran across 42nd to 12th Avenue and then backtracked to Javits. The Q32 was still the M32 and there was no M98. The Q ran on Broadway, the K ran on 8th, and there was no 9 train. The MTA logo was an M in a circle with SURFACE under the M.
The one for the M104 dates from 1992. The 57th Street triad -- M30, M57, M58 -- was in effect. The Q32 and M98 appeared. The crosstown buses from 79th Street up were the M79, M86, M19, and M20. The MTA logo was an M in a circle with no text underneath.
This is an interesting way to research bus route history. Unfortunately the guide-a-ride program was only started in the early 80's, and I assume all the oldest maps were replaced when the plastic holders were replaced with metal holders.