What I was - trying - to say in my previous post, is that pre - rock days the songs had a life of their own. Is is probably because there was a standard body of songs sung by every popular/dance band singers.
For example,even though Billie Holiday was the first popular singer to make Summertime popular,it was never her song.
For example, when, say, Nat King Cole recorded it, it wouldn't be thought that he was " covering" ,in any sense, Billie's performance, but rather that he was recording a well known song written by the Gershwin brothers.