My impression is that the practice of fashion conformity unraveled around 40 years ago. While it's possible to identify characteristics that peaked in usage at various times (bold patterns on men's sport jackets in the early 1970s, padded shoulders on women's garments about ten years later), these styles weren't nearly as dominant as those of previous decades. A good example is women's skirt lengths -- short in the mid-1920s, long in the mid-30s, knee-length in the early 40s, mid-calf during the 50s, etc.

Of course fashion following was never entirely lockstep. Older women tend to shy from wearing short skirts, for instance. And I tend to maintain a preppy look when my wife insists that I have to abandon my beloved blue jeans for some occasion or another.

Then there is the matter of transitions between dominant styles. Women's bobbed hairstyles of the 1920s were anticipated around 1910 when some avant-garde gals got their long tresses chopped. That bobbed style apparently became boring to some women even before 1930 and they began to let their hair grow out. Consider the photo below.

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This publicity photo (which I cropped a bit) is of a 1929 Auburn model 120 with girls from a physical culture club of some sort providing a lot of added interest.

Note the girl on the left and compare her hairdo to those of the others. The girls on the right have the typical tight-wave permanents of the 20s, the one on the left has much longer hair that strikes me as being more "natural" and perhaps "timeless." She also lacks the boyish, curveless figure that was the height of female body fashion during the flapper era. Compared to the other two, she looks terrific, not to mention out of place given the rest of the setting.