I know 680ís COL is North Atlanta but since North Atlanta has been gobbled up by Atlanta, I call 680 an Atlanta station.
North Atlanta was unincorporated in the 1960s. The exit signs for Ashford Dunwoody Road on the perimeter used to list "North Atlanta" as a control city but that disappeared in the late 1970s.
North Atlanta was never annexed into Atlanta. It is roughly the 30319 zip code, or Brookhaven--in DeKalb County, not Fulton.
Didn't Ring Radio actually have their studio (and maybe their transmitter) in this area (Oglethorpe/Peachtree Road south of PIB and Chamblee) back in the day, hence 680's COL? I know that 680's current array near Spalding and Winters Chapel was not their original transmitter; I seem to remember it being built sometime in the 1970s.