"The term "oldies" was popularized by Art Laboe, whose "Oldies but Goodies" albums in the 60's...."When anything other than currents began to be played on Top 40 stations... somewhere in the mid-60's, the "gold" or "flashbacks" were all from the Rock 'n' Roll era, generally going back to the later 50's. Few played early 1955-1958 Top 40 hits as even then they sounded "dated" to PDs.
The term "oldies" was popularized by Art Laboe, whose "Oldies but Goodies" albums in the 60's. In fact, he trademarked that term, and it took a while for stations to use just "oldies" for fear of a TM violation.
Art Laboe - Wikipedia (Very incomplete, particularly on the Oldies but Goodies albums which were his biggest project for many years).
Those LPs were, and are on CD, up-and-down affairs. A number of re-recordings or maybe originally rejected masters are on them. They are inferior, sometimes deeply, inferior to the actual original hit versions. At the College radio station, we have a number of these and I've marked all of the non-original hit recordings so that, hopefully, no one will play them.