and there was no commercial 12 inch release for "Rock Your Baby" upon it's release, but the label did issue one when the 12 inch craze kicked in, I know, I own one;
no one cares what the first ever 'disco' single was, they care about successful records, the ones that broke through on 77WABC MusicRadio in the early days, and those were the first Barry White hit and "Rock The Boat",followed by George AND Gwen McCrae(Rock Your Baby and Rockin Chair)
What WABC or any top forty station played meant zero to the evolution of disco. WABC and all other top forty stations usually went on a disco record after it had been played to death in clubs for six to nine months. By the time a top forty station played a disco record, it was old news. A better radio indicator for disco records was what the black stations were playing. The black stations usually were influenced by what was being played in the discos and the reports from the record pools. There were very very few disco records that became top forty radio hits versus the many many that were being played in discos and on black radio. As an aside, when WABC went heavy into playing disco records on the air, it was a last ditch pathetic attempt to stop the bleeding (WABC's ratings decline to WKTU). WABC never recovered from this disco experiment courtesy of Glenn Morgan as the ratings declined further and they changed format a few years later.