Buyers do it. Editors do it. Casual observers do it. I do it, sometimes multiple times a year. And by “it” I mean pin down a runway trend to a decade—or rather, a stereotype of one. Drop-waist dresses? Twenties, of course. Linebacker shoulders? Eighties. But if fall 2015 has taught us anything, it’s that each decade has myriad faces and isn’t, say, one big glittery Lurex-wearing cliché.The thought came to mind mulling over the season’s big ’70s motif, which sprinted out of the gate during the New York circuit and ran the full marathon to the finish line, still vigorous, in Paris. Sure, everyone’s talking about how the ’70s is a trend, but what does that mean, really? There was no singular, definable look but a range, and oh, what a range: bohemian babes who lingered from the ’60s; the era’s culture clash of Occident and Orient; the cool rise of sportswear, with its