The Siegels have recaptured the rights to the following Superman material: Action Comics #1; Action Comics #4; pages 3 to 6 of Superman #1; and the first two weeks of Superman newspaper strips.
The judge's reasoning is as follows:
There is evidence (provided by Denis Kitchen) that the Superman story in Action Comics #4 (about Superman's exploits in a football game) was sufficiently developed by Jerry Siegel and Russell Keaton some years before Action Comics #1. As such, the story in Action Comics #4 can not be "work for hire". While there is proof (based on surviving Siegel notes and documentation) that Siegel had the ideas for some of the stories of other early Action Comics issues some time before 1938, the judge says that a mere idea is not subject to copyright.
Pages 3 to 6 of Superman #1 were also developed before Siegel's and Shuster's relation with DC, so they would now belong to Siegel's heirs. There is evidence that pages 1 and 2 are work for hire, since they were done at Detective Comics's request. (The rest of Superman #1 consists of reprints of early Action Comics stories.)
But what is probably most important is the ownership of the first two weeks of Superman newspaper strips.
(This is the most complicated part of the judge's opinion, examing in detail the deal between Siegel & Shuster, Detective Comics, and the McClure Syndicate; and also citing previous cases such as the DC-Fawcett lawsuit for Captain Marvel/Superman, and a legal dispute between Burne Hogarth and Edgar Rice Burroughs, Inc.)
The judge writes (page 85):
A fact not lost on either party or the Court is that potentially valuable copyright elements subsist in this material, as it is the first material in which Superman's home planet of Krypton is named, Superman's Krypton name is revealed, and the circumstances surrounding Krypton's destruction are revealed. [Emphasis mine]That's right, it seems these key elements of the Superman franchise would now also belong to the Siegels.
So while gaining the copyright to a mere handful of Superman pages and strips wouldn't seem that important at first glance, gaining the copyright to "Krypton" and "Kal-El" seems to be a very important legal victory for the Siegels.
During my quick read of the 99-page document I found some additional and interesting details about other aspects of the negotiations between Siegel & Shuster and DC. One example: the origin of the mysterious "Lois Lane, Girl Reporter" strip is revealed. On page 23 it is stated that this strip was produced directly by DC as "filler" material due to lateness on Siegel's and Shuster's part in providing strips for the McClure syndicate. There was a side agreement (apparently done without Siegel's and Shuster's knowledge) between DC and McClure in 1943 for the production of these strips, and the cost of producing this material was to be deducted from the gross receipts of the Superman syndication (resulting in, I assume, less income for Siegel and Shuster).
Besides being happy for the Siegels, I also find it very entertaining to see details like these (and many others regarding contracts, page rates, and other financial matters) to be finally revealed in these court documents.
The initial Superman newspaper strips can be seen here.