I really thought this would be more factual. What you have mostly is that actresses claim how brave they were in appearing nude on film, others claiming the nude scenes were sprung upon them as a surprise, directors claiming the scenes they shot were edited to make them sexier. Apparently none of these nude shots were in the script and no one knew about it until the day of the shoot. Reference to obscure films doesn't really show any kind of trend. Also, although many actors (men) appeared nude in films, none of them were interviewed to see what they thought of appearing without cloths. If you ever saw the way a film is actually shot it's pretty hard to claim surprise when there are many cameras, lights, microphones, and staff around.
