This particular source is apparently well-known -- it is cited in http://www.ipwatchdog.com/2014/08/05/happy-birthday-to-you-copyright-challenged-in-class-actio

This particular source is apparently well-known -- it is cited in http://www.ipwatchdog.com/2014/08/05/happy-birthday-to-you-copyright-challenged-in-class-action/id=50684/ http://www.ipwatchdog.com/2014/08/05/happy-birthday-to-you-c... as the first publication of "Happy birthday to you". If you could find other works much older than 1922, that would be very interesting.