Just because something is long out of fashion doesn’t mean there won’t be people dressed that way. Hippydom is long out of fashion but there’s still enough tie-dye dinks to load up the Rainbow Gathering every year. So long as what the people are wearing isn’t from AFTER when the movie takes place I don’t care.
Of course there are anomalies, but it is ridiculous to have -for example - the majority of characters in a "riverboat" interior scene dressed up like someone's idea of an antebellum Natchez dandy when a film is set in the 1890's.