I distinctly remembered that NBC mostly was the network for crime dramas and not much sitcoms in the late 70's. Just Sanford and Son, Chico and the Man, and then some that came and went abruptly. Shows like the Rockford Files and Police Story stood out more just as the anti gun and anti violent movement came into play fueled by the previous decades counter culture values. That might of had something to do with it.
It was not until the 1980's when shows like Different Strokes, Facts of Life, Cosby, Cheers, Golden Girls, Empty Nest, Hello Larry, and even Nurses came into play. Even Taxi, which came in the 80's as in the 70's the ABC network had it. These were the memorable moment shows that NBC proved popular with, but were not in the 70's.