When it comes to suing the US (or a state), just remember the default answer is "you can't sue the US" (or a state), and every other case is an explicit congressional exception, like the federal tort claims act, etc.
(see, generally, https://www.law.cornell.edu/anncon/html/art3frag41_user.html...)
Surprisingly I can't find much on the case online (Some links below), and my Grandfather doesn't like to talk about it too much (though I have a box of legal documents from the case plus some articles). You can find more by looking up Edward Sohmers and the Marlin Toy Company.
https://library.cqpress.com/cqalmanac/document.php?id=cqal75...
https://books.google.com/books?id=cyU_fdnWhD8C&pg=PA22550&lp...
Even if ratified today, I doubt Zen could use it as it was not law at the time of the action.