"or blues music" It was rare to leave the V out in blues. For instance people sometimes used I-I-I-I-I-I-I-I-V-V-I-I or very close to that, but it was rarer to swap that, to include the IV and leave out the V.

There were (rarely) some 8-bar I-I-I-I-IV-IV-I-I blues, such as "Pretty Mama Blues" by Cannon's Jug Stompers, "Sundown Blues" by Alec Johnson, and "Carroll County Blues" by Narmour and Smith.