from designer to designer

... what do you think of auctions/designers who use the "don't be a copycat" with designs that are decades old? I mean, pillowcase dresses for instance, my mother made them for me as did her mother for her... yet I still see from time to time "DON'T BE A COPYCAT". Does the self-titled "original" designer have a foot to stand on here? Do people really take this to heart or go ahead & develop their own style? Thoughts?