Pianistimo is probably thinking of Irving Berlin, who could only play in C (or was it F#) and had some sort of mechanical transposer and a musical secretary to write his songs down, he did not read music well if at all. OTH Gershwin got his start in music as a song plugger, playing sheet music in stores on demand for customers who might want to buy the song. Berlin was on the other side of performing, he was a singing waiter before becoming a succesful songwriter.