I have to put in my two cents on Barbie and Ken underwear.
Some of the Barbies I remember from the early 90s did have built-in underwear like Ken. The piece that makes up Barbie's crotch area had a raised pattern on it to make it look like an underwear pattern. Sometimes that piece of the doll was flesh colored but sometimes it was white. This photo is black and white but you get the idea: https://s-media-cach...da895ea1f06.jpg
It seemed to vary depending on the specific Barbie, there would be ones without underwear right along with ones with underwear. Also, some Ken dolls did not have underwear, just an extremely vague bulge, probably not unlike a male store mannequin: https://ewgreenlee.f...03/ken-doll.jpg
I don't know which version was more common for who, but there didn't seem to be any rhyme or reason as to who had built-in underwear and who didn't.