@Kichae @rysiek And I can bet you'd find cases where the estate got screwed out of the rights too.
Most likely because the creator never actually owned them to begin with, that happens a lot.
EDIT: Remember how I said I bet there'd be cases?
Search for 'Jack Kirby Marvel copyright'. Or even just 'Marvel copyright estates'.
They're trying to pull the same thing that Disney is pulling on living creators, but they're going after the estates of some of the creators who basically made them, all of whom are deceased too. And I bet it's in no small part because those creators aren't able to defend themselves or provide their own information anymore.
(Jack Kirby's estate's case started around 2009-10 and took until 2014 to settle, but part of that was that the estate had to withdraw a petition for a higher court review of a 2011 ruling that agreed with Marvel. https://www.reuters.com/article/us-usa-marvel-kirby-idUSKCN0HL2EZ20140926)
It's actually kind of fascinating, it's drawn a ton of attention because it all hinges on some details of a 1960 ruling to do with The Game of Life and a review of that ruling for clarification. Depending on what that outcome is, it could affect... well, virtually everything copyrighted before 1976 (which would be covered by an earlier version of the Copyright Act). https://www.hollywoodreporter.com/business/business-news/how-the-supreme-court-could-shake-up-disneys-spider-man-plans-1235065460/
But I guess everyone post-1976 is kind of screwed if they didn't go out of their way to secure the rights, since it seems like the work-for-hire test is extremely broad.