"Anyway, did Calt or does Wald (or does Karl Hagstrom-Miller) have actual credible evidence that pro musicians helped invent blues music: Nope."

And bear in mind that pro musicians' activities were being documented far MORE (e.g. we know that "Stack O'Lee" was performed by black pianist Charlie Lee in 1897, "I'm Going To Start A Little Graveyard Of My Own" was sung by black minstrel-show performer Billy Cheatham in 1900, "Chicken Can't Roost Too High For Me" was sung by black minstrel-show performer C.W. Bebee in 1905, etc., because of vintage newspaper articles) than folk musicians' activities were being documented during the relevant period.