I remember sometime in the late '60s or early '70s John saying that he kept the charade going because there were 300 people in The Beatles' organization plus their families who had become dependent on it and would have starved if he didn't.
WOW, some of you sure know your business. Linus you made some very interesting observations about the piano. In his book "THE MACS MIKE McCartney's FAMILY ALBUMN" Copyright Peter Michael McCartney 1981, Paul's brother says (there are no pg.#'s in the book):
"Encouraged by father Joe, another of Dad's great loves was music, and after teaching himself chords on the second hand 'Nems' piano, given to the the Mac's during World War I, he formed the Masked Melody Makers (Mmm!)."
Father Joe would have been Paul's grandfather.
There was always a piano in their home and the book shows pics of Paul hammering away on a set of drums. So drums and piano wouldn't have been foreign to him.