////My theory of what happened in the US North after WWI would be that the young people were able to buy records for themselves and early swing appealed to them as dance music, which was a socially acceptable and effective way to court! At least in Chicago, in the early '20's,the Austin High Gang was learning to play jazz as soon as they get instruments and were playing for dances at the Columbus Park pavilion as soon as they learned the songs!
The older folks stuck more with vaudeville, but the young folks were hip as soon as they could wind up the old Victrola.////

I'm not talking about when jazz showed up, although it showed up way before the Austin High Gang. I'm talking about how early the concept of swing was known to the general public. And it appears it was known far earlier than our histories are willing to admit. Not just the concept of swing but the very word itself. Not only that but the earliest artists to use it were white. That's not to say whites invented it but it shows how well known it was from a very early period by the public.

Another example is scat-singing. Who invented it? I've had people with degrees in music tell me authoritatively that it was Louis. It was not Louis. The earliest recorded example we have of scat-singing comes from a 1922 recording by a white singer named Cliff Edwards who was also known as Ukulele Ike. He was extremely popular in the 1920s. When his career waned in the late 30s, he did cartoon character voices. In 1940, he was cast by Disney to do the voice of Jiminy Cricket in "Pinocchio." Despite his extreme popularity in the 20s, most people today have never heard of Ukulele Ike or know that he recorded the original version of "Singin' In the Rain" (1929) but everybody knows his version of "When You Wish Upon a Star." But Cliff was scat-singing at a time when Louis's career was just getting started--and he wasn't singing at that point in his career.

To go back even earlier--1915 or 16--a white singer name Gene Greene did a ragtime song called "King of the Bungaloos" which consisted of him "cooking" his voice to sound very gruff as he mouths long strings of nonsense syllables. The resemblance to Louis's scat-singing is a bit startling. If Greene's song isn't scat, it is forerunner. But when are Greene or Edwards ever mentioned when it comes to the invention of scat-singing?

You see how PC thinking is skewing our knowledge of history?