Jean, Peter Sellers told a story of his early days as a drummer in a jazz band (immediately post second world war)

"This rather obnoxious customer came up to the band and asked -nay demanded- we play "That's What You Are". The bandleader hummed and hawed a bit, and finally said "look, we don't know the song, sorry" The customer became irate, "Of course you know it, how much do I have to pay you to play it?" The bandleader tried to calm him down a bit. "Look could you sing a bit of it, and maybe we'll try to fake it"?
The customer opened his mouth and sang "Unforgetablllllle...THAT'S WHAT YOU ARE....!!"

Fats Waller apparently used to go into the various Tin Pan Alley music Publishers' offices, jam a bit on the piano, and collect advance royalties for "New songs under construction". Once he recorded two improvised Blues (one fast and one slow). When asked what their titles were he thought quickly and said "Harlem Fuss" and "Mainstreet Shuffle"...and then quickly forgot them. When the songs were later requested in nite clubs, he didn't have a clue what they were! He usually said "You must be confusing me with James P Johnson"!

'Fraid I have that old Ritchie/Clayton album as well.

Cheers

Rick