When do IP rights in an original work that is supplemented by others no longer hold?

Donald Duvall, former chief administrative law judge for the International Trade Commission, while subsequently working for Kenyon & Kenyon, wrote a treatise on proceedings before the commission involving Section 3378 of the Tariff Act of 1930.

In 1997, Duvall entered into an agreement that gave Kenyon specified editorial rights over the text, and established that one-third of the royalties generated by the work would go to Duvall or his estate, as long as his name was included. Updated editions (including that published in 2011) credit Duvall as the original author.

Duvall died in 1999. His estate continued to receive royalties for more than a decade.

In June 2012, Kenyon & Kenyon notified the widow that the estate wouldn't receive future royalties because there was "virtually nothing left" of Duvall's original text.  In a complaint filed on April 17, Kathryn Duvall demonstrated that much of her husband's work was included in the latest version and accused the firm of trying to deny the estate its rights before the publisher released an electronic version—"a source of sales that will generate substantial revenue and thus substantial royalties," she claimed.”

The case has import to all publishers that update original works, creating supplements or new editions, as well as valuators who need to assess risk associated with such copyright properties found in estates.  When does an original work no longer have the characteristics of the original that would serve to enforce IP rights of the original author? If the author refuses to supplement the work (or is unable to supplement it), at what point do rights in the original dissipate?

The case is assigned to U.S. District Judge James Boasberg, District of Columbia.