From what I know about being trans back in the day, they used to basically make you cut off all contact with anyone who knew you prior to your transition in order to access hormones/surgeries, and fully start your life over in a new place, so that none of the new people you met would have any idea you were trans. So there definitely were more trans people than anyone knew about, but no one knew their histories because they categorically did not disclose to anyone. (Correct me if I'm wrong, I was not alive in the 70s)