I think they were still called Championship dirt cars well after the 1971 separation. IIRC they changed it in the early or mid 80's when USAC made some champ dirt races like Indy, Duquoin, and Springfield count toward the "Gold Crown Championship" which also included the Indy 500. The remaining champ dirt races were then named the "Silver Crown" division. After a while the 500 was the only Gold Crown race left. Eventually Gold Crown went away after a few years and that just left Silver Crown.

Correct me if I'm wrong, but Mark Alderson had a lead in the Gold Crown points one year and needed a ride at the 500 to secure the championship and couldn't find one.