Been a curiosity for me also, who taught the old guys. According to popular legend, the accordion didn't make it to SW La til around the turn of the century, but by the 20's, we guys playing incredibly, just from recordings, and no telling how many unrecorded. So how did they learn to do all that cool stuff that I still can't do after studying them on electronic playback over and over and with youtube.

I shall post my findings soon on how they did it. Doing some serious study on the matter. Almost feverishly. LOL