I'd recommend to all readers that you watch this video, taped inside the Times Square subway station in the '80s. It's interesting to see what looks the same and what looks different. Of course, the most notable difference is all of the graffiti on the trains!
Also - there was a "K" train?! Where did that go?
I'd like to find some videos from even earlier than that; if I find any good ones, I'll share those here as well. If you know of any, let me know! I'm very interested in the different stages of the New York City subway system.