I guess we weren't recording the WNEWs and WLWs of this world as teenagers. Definitely a lot of radio history has been lost.Even in the 1960s, there were different strains of MOR. Billboard used the terms pop-standard, standard and conservative to describe adult music stations. It appears that conservative is the term used to describe stations that would eventually be called beautiful music.
Seems like most markets had a MOR that was always a little more contemporary even if that meant Andy Williams, Frank Sinatra and Tony Bennett. Even before KMPC went to a more AC approach in 1973, I think they were always a little “heavier” than KFI (1968 maybe the exception). Same with WNEW vs. WHN or WIND vs. WMAQ or WIP vs, WPEN.
The full service stations that played even less music than the KMPCs of the world also seemed to have very easy listening overnight programming: WGN, KMOX, WJR, WCCO etc. Some carried shows like Dolly Holiday (WBAL) or Music Til Dawn (WLW, WCBS, WBBM) which mixed in semi classical selections.
While 1960s top 40 is well preserved especially the WLS and KHJs of the world, it is too bad that so few adult radio stations of the era exist on airchecks. Not to mention country and ethnic formats.
I remember some very uptempo A/Cs with top 40 formatics but all the news, weather, traffic etc. Both WTVN and WBNS, Columbus, OH, WVLK and WLAC , Lexington, KY for a couple of markets.