Longest lasting logos for the Big Four US TV networks

The Big Four comprising of NBC, CBS, ABC and Fox. NBC's longest lasting logo was used from August 26, 1985 to September 30, 2013. CBS' longest lasting logo was used from 1966 to March 1, 2021. ABC's longest lasting logo was used from October 19, 1962 to September 10, 1988. Fox's longest lasting logo was used from September 1, 1999 to August 1, 2020.