Judging from the first advance promo photo of the last run of “Mad Men” episodes, the costumers are taking their cues not so much from the 1960s/70s as they are from 60s/70s era “Legion of Super Hero” comic book. The first thing I thought of when I saw Jessica Pare (a.k.a. Megan, a.k.a. the ex- Mrs. Draper #2) was 'It’s the Phantom Girl. Meanwhile, Sally certainly looks like she’s rocking a dress in that Duo Damsel wouldn’t have seemed out of place wearing.
Having been born in May of '69, I don’t quite remember the early 1970s. But did girls / women really dress that way back then? I remember bell bottoms, clogs, and quasi-hippie fashions, but those clothes look a little strange.
I wore little dresses and also blouses with those sleeves, that Sally is wearing in the picture. They were called leg o’ mutton sleeves and it was a fashion taken from Victorian times, for a while. (I had a sewing pattern and I made a blouse like that, with insets of lace. It took forever to make, but I was so proud of it!) My skirt was absolutely that short, and I well remember the textured hose! Also fishnets, and little flat patent leather shoes in every color.
Megan’s white lace crop top and pants outfit - reminds me of outfits on the Sonny and Cher show. I also had those sleeves, 3/4 length with the ruffle, on dresses and blouses (but not the midriff look).