WARM in Scranton has always been WARM, even before Susquehanna's ownership. They bought it from the Scranton family, among whom was William Scranton, one-time Governor of Pennsylvania. There even was a short-lived WARM-TV in the 1950s. There was never a WARM-FM in Scraton, however. While the same call letters, with -FM or -TV attached, could be used by co-owned stations in the same market, this was not allowed for co-owned stations in separate markets until the 1980s. Now, of course, stations owned by completely different companies can use the same calls by agreement, but there can still be only one station of each type, AM, FM or TV, using the calls.
As I recall, the FM in Atlanta was WLTA, and renamed WARM-FM when it flipped to soft AC. Although 103.3 in York called itself "WARM," it was still WSBA-FM until the Atlanta station changed format and calls to WAPW. Several of Susquehanna's easy listening FMs flipped to soft AC in the 1980s and adopted the "WARM" name, although their calls were often variations like WRRM or WWRM. The exception was WMGS in Scranton, which they called "Magic" so as to differentiate it from the AM.