"The "smoking gun" is a 1927 version of the "Happy Birthday" lyrics, predating Warner/Chappell's 1935 copyright by eight years. That 1927 songbook, along with other versions located through the plaintiffs' investigations, "conclusively prove that any copyright that may have existed for the song itself... expired decades ago."

Filmmakers fighting “Happy Birthday” copyright find their “smoking gun” : https://gnusocial.no/url/15642

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