In Phoenix, for instance, the first Oldies station calling itself that was probably KOOL-FM in the very late 70's or early 80's.
KOOL-FM became an oldies station absolutely no later than August 1973 (and I think it was 1971 or '72 when that format started). That's when I moved here for college, and it was oldies then.
There were one or two AM's that played some classic RnR but I don't remember them using the term Oldies (KOPA which was KOOL's AM side and another I can't recall at the moment).
KOPA was 1440 and 100.7 for many years. I don't think 960 was ever called KOPA. KOOL 960 had a satellite-delivered oldies format in the '90s that I think it originated, but was not a simulcast of 94.5.