There isn't any good evidence of how many times Joplin played at the Midway. Most of the evidence is from interviews decades later. Similarly, we actually don't know what kind of music his band was playing. It could have been early rags, but if they were, they didn't make waves the way lots of other art and ideas that debuted at the fair did. Certainly, ragtime was not associated with the Fair in subsequent memory.
In next week's post I am actually going to discuss the way the fair is considered the beginning of certain ideas (in urban planning specificalyl) that already existed—but maybe need a big white puffy outfit to truly debut.