A well deserved congratulations, my good man.

Philo

I haven't read the whole book yet, but the early chapters don't speculate on the term "pennywhistle". Sales flyers in the early 1900 still called them "Clarke London Flageolets" or "Clarke Flageolets". By 1903, they were $1.35 a dozen, so considerably more than a penny. in 1953, George Goddard (some relation to Clarke's wife Sarah Goddard) wrote in the Oldham Chronicle "...one of his conceptions eventually developed into the making of the first Pennywhistle as we know it today..."

I've done some research and determined that while the words "penny-whistle" and "tin-whistle" both predate Clarke, neither were likely in common use until later in the 20th century.

Ooops!

OED = QED!

Thanks for upsetting the whistle-cart

Sorta. The OED doesn't reflect common usage, and I'm still curious about that. As best as I can tell, neither term was common until well into the 20th century, but I'm still looking for definitive evidence on that.