Attorneys for suing filmmakers uncover a blurry version of an 88-year-old book in the files of Warner/Chappell. That leads to another serendipitous discovery.

On the eve of a judge's ruling, attorneys find key evidence tucked away in the files of the opposing side. They rush to court with word of their bombshell discovery. If this sounds like the third act of a Hollywood movie, it very well might become one.

The filmmakers working on a documentary about the world's most popular song, "Happy Birthday to You," and currently suing Warner/Chappell for the right to use the song in the documentary without any license fee, filed court papers on Monday touting newly uncovered evidence that "proves conclusively that there is no copyright to the Happy Birthday lyrics."

The "proverbial smoking gun," as the plaintiffs put it to a California judge, is a book of children's songs that comes straight out of Warner/Chappell's digital library.

Betsy Manifold and Mark Rifkin, attorneys for the plaintiffs, were only given access to these files just three weeks ago. They were told the documents were held back "mistakenly." What they found was a blurry version of the 15th edition of The Everyday Song Book, published in 1927. The book contained Happy Birthday lyrics. Intrigued by the discovery, and looking for a cleaner version, the lawyers started hunting down earlier editions, and in the archives of The University of Pittsburgh, they came upon the fourth edition, published in 1922, which included the famous Happy Birthday song without any copyright notice.

This book, plaintiffs believe, establishes that "Happy Birthday" lyrics were dedicated to the public years before the copyright registration that Warner/Chappell is relying upon was made.

If this proposition is accepted by the judge, Warner/Chappell may lose out on a cash cow that is reported to reap $2 million a year in revenue. Filmmakers like the named plaintiffs — and others who have forked over as much as six figures to license — would no longer have to pay a penny to feature "Happy Birthday" in motion pictures and television shows.

Good Morning to You Productions Corp., run by director Jennifer Nelson, filed the class-action lawsuit in 2013 after being told she'd have to pay $1,500 to use the song in her "Happy Birthday" documentary. After first being reported by The Hollywood Reporter, news of the litigation spread across the globe and was called the "lawsuit for the ages" by The New York Times. "It went viral and I never thought it would happen like this," said Nelson in a speech last year.

The legal action, like Nelson's pending film, puts a spotlight on a song that traces its origin to work by a schoolteacher named Patty Smith Hill and her sister Mildred Hill.

The Hill sisters later assigned rights to a publishing company owned by Clayton Summy. Later, copyright registrations were made by Sumny's company on "Happy Birthday." Warner/Chappell has been contending that the 1935 registration covers both the piano arrangement as well as nearly universally known lyrics.

The parties have engaged in nearly two years of debate over such topics as the possibility of fraud and whether decades-old letters about the origins of the song were protected by attorney-client privilege. After extensive discovery, both sides made summary judgment arguments last winter with U.S. District Judge George King requesting extra briefing on the issue of whether the "Happy Birthday" copyright was abandoned. Warner/Chappell has argued it wasn't abandoned unless the Hill Sisters published or authorize others to publish their works prior to the 1935 registration. The song publisher said there was no such proof of that.

Now, just as King was set to either blow out the candles on this litigation or deliver a gift to those wishing to make free use of the popular song, the plaintiffs have stepped forward with some dramatic flair.

The next oral hearing in the "Happy Birthday" dispute is scheduled for Wednesday. And so, the new filing comes at the judicial equivalent of a few minutes before midnight, so late that King had previously ordered the parties not to supplement the record with new evidence. The plaintiffs say they have good reason anyhow — the "smoking gun" only recently being obtained from the other side — to come forward with their serendipitous discovery.

According to their application for the judge to consider this new evidence, "Because the 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 — indeed, all those issues become moot — Plaintiffs are compelled to bring them to the Court’s attention now, before more time is needlessly spent on the pending Summary Judgment Motions and before the oral argument scheduled for July 29, 2015."

Here's plaintiff's latest court papers.

Randall Newman, one of the attorneys for the plaintiffs, says Warner/Chappell "should admit defeat but they won't because too much money is at stake."

UPDATE: Warner/Chappell has submitted its response in court. The publisher is not opposing the plaintiffs' request to supplement the record, but say "at most, the documents would create an issue of fact whether The Cable Company," the company that put out The Everyday Song Book, "made a publication in 1922 that could have divested the copyright owners — the Hill Sisters — of their common law copyright in the Happy Birthday! lyrics."

Warner/Chappell says there's there no indication the Hill family was aware of the book nor authorized it. They write the "evidence instead shows that Summy sought and obtained a license to publish the Happy Birthday to You! lyrics" in 1935 — and "Summy would not have had to secure a license from Jessica Hill if it already had the rights to Happy Birthday to You! or if the work had fallen into the public domain."

Summy appears to have given "special permission" for the 1922 book — but in an attempt to at least let the case go to trial, Warner/Chappell asks "Was it for Good Morning to All only? Was it for that work in combination with the Happy Birthday lyrics?"

Elsewhere in Warner/Chappell's brief (read here), the defendant attempts to explain why it took them so long to hand over this key evidence. "Warner/Chappell was not hiding that or other documents or proceeding in bad faith," write their attorneys, explaining that it didn't believe documents from its "work product factual investigation" were "subject to discovery" until the March summary judgment hearing, a new review of files and so forth.