Hollywood movies put actresses into 1880s-1900s corsets for the "sex" without the exposure. Actresses could appear undressed without being more undressed than a bathing suit. The costume looks like something with a short skirt with pants underneath or short pants and the corset. It looks like the one piece bathing suits from back in the mid 1900s. Geeeeze! I remember thinking those looked hot then.
Janet Leigh doesn't even wear the black outfit in the movie Naked Spur that the shots are publicity for. Basically she's wearing 1950s underwear with guns and that's OK.These were costumes based loosely on the actual corset worn over the chemise without any pants underneath.
Here is you really be seeing if the movies were "correct". You may note that the garters attached to the corset will not allow any kind of pants to be worn easily underneath.
What was sexy about the photos and images of the actual clothing (considering the some were posed by the artists and photographers) was that even dressed, there was no garment left in the way of having sex, even if that detail wasn't clearly shown. The viewer just knew. The movie versions still included some garment that covered the actress making it "OK" for the audience or censors.
Madeline Kahn in Blazing Saddles.