Yes, Patricia Field did exist before Carrie Bradshaw.
Back in the Gays just unearthed this mid-1980s video of the Patricia Field shop, long before it moved to the Bowery. (Their site has more info on who's who.)
Check out all the '80s "Attitude," as New York magazine called it in 1982, when Patricia Field's shop was outfitting youth culture in "high-topped black sneakers, prom jackets, tutus, polyester suits, pointed vinyl shoes, and Hawaiian shirts." (At the same time, "Fern bars and sushi have spread to the East Village [where] gentrification is sending rents skyrocketing, despite the local Hell's Angels coven and the legion of Bowery Bums.")