"How are YOU defining what is or is not BLUES?"

The same way blues fans generally do today, which is the same way black blues musicians born in the South in roughly 1900 generally did. It only became fashionable to sing about having the quote "blues" among black folk musicians (before it became fashionable among anyone else) in about 1907, in songs that were very similar to first-person songs that had sad lyrics and did not have the word "blues" in them along the lines of "Poor Boy Long Ways From Home" and "All Out And Down." I'm calling all those types of songs blues songs. Mance Lipscomb recalled hearing "All Out And Down" in about 1909, and Gus Cannon recalled hearing "Poor Boy Long Ways From Home" in roughly 1900.

"Is there documentation of the actual music heard by Maggio, Kennedy and Perrow?"

Maggio and Kennedy yes, Perrow no (and it wasn't Perrow who heard blues in Missisippi in 1909, it was a guy named Aldrich who provided lyrics to Perrow for an article). Maggio said he based the 12-bar section of his instrumental "I Got The Blues" on the 12-bar strain with the same title that the black guitarist played on the levee in 1907, and that section is 12-bar blues musically. Kennedy heard a variant of "Poor Boy Long Ways From Home" sung by blacks on the streets of Gretna, Louisiana, and included it under the title "Honey Baby" in his book _Mellows_. Perrow's article gave lyrics (about having the "blues"), and the lyrics were very similar to blues lyrics collected independently by Odum before 1909.

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