What's interesting about Cosby only being in the first season (which would have been 1971-1972) is that I recall quite a few of his skits. So I either have a really good memory (since I was only ages 4 and 5 those years) or they replayed his skits after he left the show. He was such a natural when it comes to kids. Loved that one on SS I brought up before where he says, "Hi I'm sitting here with my three friends."
I know this comment’s 20 years old so no surprise if there’s no reply but Cosby only left the regular cast after season 1, but season 1 wasn’t his only season with the show. He left the show in 1973 like Lee Chamberlin did. Cosby was still a cast member in season 2, but he wasn’t a regular cast member. He occasionally appeared in new segments he mostly taped himself during season two’s production. Most of Cosby’s segments in season two were similar to the celebrity guest cameos taped during that year as well, but Cosby also appeared with the cast during that season as well (he appeared in “A Very Short Book: Old King Cole” with Luis Avalos, Jim Boyd, and June Angela, with Melanie Henderson narrating the skit), which is why he was credited as cast in season two as well as season one. Luis did replace Cosby in the regular cast in season two, but season two was Cosby’s official last season on the show entirely as a cast member.