I lived in Selma Alabama in 1966-67. It seemed pretty rampant to me back then...
Heck, we were a WHITE family, but my Dad was military and thus associated with the federal government. In Selma in 1966, we literally could not get served in a restaurant. No one would ever serve us. We pretty much ended up living on the base and driving THRU Selma to go elsewhere.
Racism was still very strong in the 50s & 60s.
Cosby was rich and famous by 1966 and immensely popular in America, he wasn’t born or raised in the deep South, he is from Philadelphia.