Further investigation showed that the song appeared in editions stretching back to 1922, which in the plaintiffs' view "proves conclusively" that "Happy Birthday" entered the public domain no later than that year. The song was printed without a copyright notice unlike other songs in the book. Rather, it included a notice that read "Special permission through courtesy of The Clayton F. Summy Co."
That important line of text published underneath the song's lyrics was "blurred almost beyond legibility" in the copy that Warner/Chappell handed over in discovery. Plaintiffs' lawyers note that it's "the only line of the entire PDF that is blurred in that manner."
If you haven't been following the issue closely, there is actually a lot of evidence, much of it put together by Robert Brauneis, that the song really should be in the public domain. There are all sorts of questions raised about how it became covered by copyright in the first place. Everyone agrees the song was originally written as "Good Morning to All" in the late 1800s, but from there, there's lots of confusion and speculation as to how it eventually was given a copyright in 1935, granted to the Clayton F. Summy company. People have argued that the 1935 copyright was really just on a particular piano arrangement, but not the melody or lyrics to Happy Birthday To You -- which had both been around long before 1935.
This latest finding at least calls into question how honest Warner/Chappel has been for decades in arguing that everyone needs to pay the company to license "Happy Birthday" even as the song was almost certainly in the public domain.
This would be a pretty big shake-up, especially if Warner/Chappel were ordered to retroactively pay back license fees if it's proven they had knowledge of all this. Regardless, the fight over “Happy Birthday” is becoming the music publishing world’s equivalent to a juicy detective novel.