I finally got a look at the ancient map at the 57th Street station. It's kind of hard to find, since it is on the back of one of the plastic panels for the new maps. Unfortunately, there's a plexiglass booth wall in front of it, so it's difficult to get a good picture of it. I tried with a flash and without, so we'll see what happens. It looks to be the sytem in the mid-Seventies, after 1973 (when the Third Ave El was eliminated in the Bronx) and 1978 (when they got rid of the double letters).
Of additional interest is the presence of two honest to Betsy phone BOOTHS, with doors that close.
BTW, 57th Street seems to be the apex of 1960s utilitarian subway design. The mezzanine is cavernous with relentless gray paneling, and the platform tiles are the same uniform stuff they defaced downtown IRT stations with, only colorless. The message is. "Move along. We're here to collect fares, not be a part of this Fun City/I Love New York business".
www.forgotten-ny.com