It's been two years since filmmakers making a documentary about the song "Happy Birthday" filed a lawsuit claiming that the song shouldn't be under copyright. Now, they have filed (PDF) what they say is "proverbial smoking-gun evidence" that should cause the judge to rule in their favor.

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."

If the filmmakers' lawyers are right, it could mean a quick route to victory in a lawsuit that's been both slow-moving and closely watched by copyright reform advocates. Warner/Chappell has built a licensing empire based on "Happy Birthday," which in 1996 was pulling in more than $2 million per year.

Plaintiff Jennifer Nelson's movie is actually called Happy Birthday, and it's about the song. She had to pay Warner/Chappell $1,500 to use the song in her movie, and that didn't sit well with the documentarian. She's seeking to get that money back and also represent a class of plaintiffs who have paid similar licensing fees to Warner/Chappell on a copyright she and her lawyers say is illegitimate.

The 1927 songbook referenced above was found in a batch of 500 documents provided by Warner/Chappell earlier this month. That cache included "approximately 200 pages of documents [Warner/Chappell] claim were 'mistakenly' not produced during discovery, which ended on July 11, 2014, more than one year earlier," Nelson's lawyers write.

The new filing comes as US District Judge George King was just two days away from holding a hearing about whether or not songwriter Patty Hill abandoned her rights to the lyrics. The plaintiffs say that the newly discovered songbook evidence is so strong that the copyright abandonment issue is moot.

"[T]he documents prove conclusively that the song is in the public domain, thus making it unnecessary for the Court to decide the scope or validity of the disputed copyrights, much less whether Patty Hill abandoned any copyright she may have had to the lyrics," they write.

Missing notice

Reading the motion is an exercise in understanding the mind-boggling complexity of music copyright.

In 1927, Chicago music publisher The Cable Company produced the 15th edition of the children's song book called The Everyday Song Book (Graded). It included the "Good Morning" and "Birthday Song," which featured the melody for "Good Morning To You," a song dating back to the 19th century, combined with Patty Hill's lyrics for both "Good Morning" and "Happy Birthday."

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."

The Summy company is a publisher whom Warner/Chappell has maintained never authorized any pre-1935 publishing of the "Happy Birthday" lyrics.

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."

Plaintiffs acquired their own copies of the songbook, including a first edition published in 1916, which didn't have the song, and versions published 1922 and later, which include it without a copyright notice.

That's critical, because under the 1909 Copyright Act which was then in force, a published work had to include the word “Copyright,” the abbreviation "Copr., " or the "©" symbol, or "the published work was interjected irrevocably into the public domain."

The plaintiffs argue that the 1922 publication without proper notice forfeited copyright in the work. Even if the judge overseeing the case doesn't agree with them, however, there's a secondary argument: the copyright for the whole 1922 songbook expired in 1949.

There's even a third line of defense: even if the work had been published in 1922 with proper notice, and even if that copyright had been renewed in 1949 (which the plaintiffs say it wasn't), the song still would have become public domain at midnight on December 31, 1997.

Warner/Chappell hasn't yet responded to the motion. Since a hearing was scheduled for Wednesday, it's likely there will be some further developments in the case later this week.

Warner/Chappell "should admit defeat but they won't because too much money is at stake," plaintiffs' lawyer Randall Newman told The Hollywood Reporter, which first reported the new motion.