Thomas, thanks for the link to my article on TMK — but I think there's a small typo in the URL you're giving. Could you fix that?

http://themushroomkingdom.net/smb_release.shtml

Frank Cifaldi got several new sources, but sadly he ran into the same dead end I did... it's quite possible to get a vague idea of when the game was released, but no one has been able to provide the "smoking gun" to prove exactly when it was first available.