One of the most common facts Kirby critics cite -- well, the ones who actually have a basic understanding of the facts of the case, anyway -- is that he sided with Marvel when Joe Simon attempted to recapture the rights to Captain America in 1966.
I'm reading Marvel Comics: The Untold Story, by Sean Howe. It's an excellent book, and recommended.
And I just came across the exact wording of Kirby's statement on the subject. It appears on page 77 of Howe's book, and he cites a post on 20th Century Danny Boy, which has a scan of the statement.
It reads, in part:
I felt that whatever I did for Timely belonged to Timely as was the practice in those days. When I left Timely, all of my work was left with them.
Kirby certainly seems to be suggesting that the work he and Simon did for Timely in the 1940's was work-for-hire and not spec work. As such, that does seem to undercut any later claims he or his family might make that he believed he and Simon created Captain America independently and had a right to terminate the transfer of copyright.
Critics of the Kirby Estate's legal maneuverings over the past few years cite that this shows that Jack knew his work in the 1960's was work-for-hire, too.
But does it?
Because from where I'm sitting, it seems to indicate exactly the opposite.
Kirby says, "I felt that whatever I did for Timely belonged to Timely as was the practice in those days." Why the past tense? If Kirby believed that the work he was doing in the 1960's was work-for-hire, that it was owned by Marvel, and that he had no stake in it -- why would he refer to that arrangement as what "was the practice in those days", decades earlier? Why wouldn't he use the present tense? Why wouldn't he indicate that this was still the practice at the time he was writing that statement, if he believed that to be the case?
Kirby's words in this document clearly imply that he believes the work-for-hire arrangement is a thing of the past, and not a standard agreement at the time he wrote the statement in 1966.