As someone who grew up and competed in the SCC in the early 80s, it was Knoxville, Pella, Chariton, Davis County, Albia, Centerville, Clarke, and Winterset. Clarke and Winterset left for the Little Hawkeye in 1983 and were replaced by Oskaloosa (who left the SE 7) and Grinnell (who left the CIC).
Then, Grinnell, Knoxville, Oskaloosa, and Pella left (95-95 school year), Clarke came back, and Eddyville-Blakesburg-Fremont was added. In 98, PCM joined; they left in 2006. In 2014, Knoxville came back, and in 2022-2023, they added Cardinal.
The conference has been in existence since 1930 and originally included Valley, Indianola, Winterset, Knoxville, and Pella.
Pella Christian would be the third smallest if they joined the SCC, only Cardinal and EBF are smaller. Even though Knoxville is considerably larger, they do not dominate the conference.