When Mahalia Jackson sings the back of a WNBC TV camera can be seen showing her name as a lower third insert on screen. TV-camera monitor only shows and transmits the text-less clean feed.
Several times, there is a reference to the subway in DC. The subway system there wasn't built until 1976.
A phone conversation shows modular plugs on the handsets...
During a part of the film set in 1963, Rustin attends a party where people are dancing to the song "Shotgun" by Junior Walker & the All Stars. The song was not released until 1965.