There may be no song more widely sung in America than “Happy Birthday,” but it isn’t free to sing. Warner/Chappell music licensing, which has long claimed copyright to the words, typically dings filmmakers and TV producers a few thousand bucks for a “synchronization license” any time the song is used in video. Warner reported that by the 1990s the “Happy Birthday” licensing enterprise was pulling in upwards of $2 million annually.

In June, a filmmaker who paid $1,500 to use the song in a documentary (called “Happy Birthday”)challenged Warner/Chappell in court. The filmmaker’s lawyers argued that the 1935 copyright isn’t valid—at most, it covers a particular piano arrangement and a second verse to Happy Birthday which has no commercial value. The melody has been around since 1893, they say, and the “Happy Birthday to You” lyrics were in wide use by the early 1900s. The plaintiffs hoped to form a class action and make Warner pay back everyone who’s paid a license fee since mid-2009.

A status update filed in court on Monday offers a first glimpse of some of the defenses Warner may use. In a brief statement, first mentioned by The Hollywood Reporter, Warner lawyers explain it’s on the plaintiffs to prove that the 1935 copyright registration “was not intended to cover the lyrics to Happy Birthday to You.”

Even if the plaintiffs show that the lyrics were published elsewhere, “this would not show that the author of the lyrics copyrighted under certificate E51990 copied those lyrics from somewhere else,” argue Warner’s lawyers. “Copyright law requires originality, not novelty.”

The burden is on the plaintiffs “to disprove the validity of Warner/Chappell’s copyright and the facts stated in the registration,” argues the defense. And that registration clearly references “words” and “text,” which they believe is the traditional “Happy Birthday” verse. Warner’s lawyers write:

Certificate E51990 applies on its face to a “published musical composition” entitled “Happy Birthday to You” and the listing under the byline is as follows: “By Mildred J. Hill, arr. by Preston Ware Orem;* pf., with words.” (Emphasis added.) The certificate further states: “(© is claimed on arrangement as easy piano solo with text).” (Emphasis added.)… All of this, as well as the validity of the copyright, is prima facie presumed true in this litigation.

The plaintiffs are claiming that the words were published in a variety of formats pre-1935. The amended complaint filed in December lays out the most detailed version of their argument.

“Even though the lyrics to Happy Birthday to You and the song Happy Birthday to You had not been fixed in a tangible medium of expression, the public began singing Happy Birthday to You no later than the early 1900s,” write the filmmaker’s lawyers.

The lyrics were published as lyrics in a Methodist Episcopal Church song book in 1911, which did not attribute ownership or identify any copyright for the song. An Indiana educator’s guidebook described children singing the words “happy birthday to you” as early as 1901, although it did not print lyrics. The plaintiffs’ complaint suggests that pre-1935 of the lyrics were, in fact, abundant: “By 1912, various companies (such as Cable Company Chicago) had begun producing unauthorized printings of sheet music which included the song known today as Happy Birthday (i.e., the melody of Good Morning to You with the lyrics changed to those of Happy Birthday).”

The parties have agreed to a schedule that has discovery on the copyright issue continuing through September of this year. Once they collect the evidence, the two sides will submit motions arguing their case in November. The copyright validity issue will apparently be decided on the papers, as the status update does not include dates for a trial or a pre-trial conference.