i think that cherry red cadillac convertible that magic drives is a '58 or '59, and LONELY TEARDROPS was released in '59. also, all of the clothes are far more 50's than 60's. by the time JFK was inaugurated, the ties, lapels, cut of suits were skinnier--the late 50's still had color and shape.
so that's my roundabout way of asking: do they ever establish the actual date in the movie?
Whenever a decade is referred to as the __'s, it seems that the reference is to the last half of that decade and the first half of the next. The first five years of the seventies looked a lot like the late 60's, the early 60's seemed more like the 50s, etc.
As for cars and fashion... people used to keep their cars for years so having one five years old was no biggie. I had a '75 Dodge Dart that was cast in a movie set in 1978. Mine was one of the "newer" ones on the set.
The latest fashions may be big for people in front of a camera or in a big cosmopolitan city. Most people are a little slower to change and that was especially true in middle class middle America. And then there was the Hand-me-downs! I can still remember male relatives bragging about how their 10 YO suit still looked like new! That was particularly gross when they were talking about an avocado double-knit leisure suit!
Skinny lapels were more from the 50s and early 60s. The mid and late 60s and all of the 70s had fat ties... fat and ugly! Really ugly! In the eighties, all my music biz friends were trying to find ties from the 40s and 50s for the skinny look and the vintage graphics.
Anyway, that's my take!
"Why can't we all just get along?"