Wardrobe people do this kind of thing all the time... I remember seeing Chicago and my friend who is a fashion design/theater major and really interested in fashion history got all worked up... she said that a lot of the things they were using hadn't been "invented" (I guess?) until a decade after the movie's settings.
I don't always notice these things. I have to wait until Factory Girl plays here! I really want to see it. We talked about Warhol a lot in a class on Modernist art I took last semester. My teacher is of the opinion that Warhol was the most important figure of the 20th century in art/celebrity, and after hearing his theory, I'm very receptive to the idea.
Also I LOVE the Velvet Underground.