In case I wasn’t clear in my OP, I was asking for confirmation that Guin’s Earthsea series on the one hand, and Miyazaki’s manga on the other hand, do not take place in a shared universe. If you’re saying that the two works actually share a character, or that Guin and Miyazaki are actually the same person, then I’m happy to withdraw the nomination of Tales from Earthsea.
There’s the movie “Julie and Julia”, based on two memoirs “Julie and Julia” by Julie Powell, and “My Life in France” by Julia Child. Obviously the memoirs are somewhat related, but were written by two different people who never met.
The League of Extraordinary Gentlemen.
It was based on a comic book series, but that comic book series drew characters from a pretty diverse set of sources.
I don’t know if drawing characters from different sources counts, when there is no melding of plots. Otherwise you would have to count Dracula vs. Frankenstein or Murder by Death (although the latter are parody versions).
I don’t know if this one counts but I think it is worth noting. The Robert Altman movie “Short Cuts” is based on a short story collection of the same name by Raymond Carver. I have heard that all the stories are unrelated but that Altman wove them all together for the movie. Eh.
There is a movie called 36 Hours that was unrelated, but similar, to a Roald Dahl short story, a fairly famous one. A part in the movie was offered to Patricia Neal, who was married to Dahl, and she found it very similar. So, while taking basically nothing from the short story, the producers acquired the rights to the story, I guess to keep Dahl from suing them. So on the IMDB page it looks like Dahl contributed.
If you haven’t seen 36 Hours, it’s a really good movie. Don’t read anything else about it including the Dahl short story until after you’ve seen it. Yes, I’m trying to spoiler a movie from 1965.
The 2010 HBO TV show The Pacific is primarily based on two books, Helmet for My Pillow by Robert Leckie and With the Old Breed: At Peleliu and Okinawa by Eugene Sledge, along with a few other books for more info such as Red Blood, Black Sand by Chuck Tatum,
Alongside the show came a companion book also titled The Pacific by Hugh Ambrose which is a general history of the Pacific theater covering the battles Sledge and Leckie were in. So three books became a minseries that became one book.
I think there’s a problem with trying to say what sources a film came from. I’ll give a couple of examples from what I consider to be great movies. The problem is first that often a film draws on sources that the screenwriter doesn’t even remember having seen or read. In some sense, any script is influenced by everything that has happened to the screenwriter or that they have read or that they have seen in their entire life. Also, sometimes the screenwriter is deliberately hiding their sources.
The first example is the 1985 movie After Hours. In some sense, it’s influenced by all the “New York as everyday horror” movies from the 1960’s to the 1980’s, including those directed by Martin Scorsese. Since Scorsese directed After Hours, there’s no reason to acknowledge this in the credits. A big problem though is that much of the plot of the film comes from a radio monologue by a performer named Joe Frank. Apparently this was not known to anyone associated with the movie except for the screenwriter Joe Minion until after it was released. Minion complained and got paid something for being a partial source for the film.
The second example is the 1984 film The Terminator. After it was released, Harlan Ellison complained that it was largely based on two episodes of Outer Limits that he had written. He was then paid for being a partial source. In some sense, The Terminator throws together ideas from a number of different science fiction movies, TV shows, novels, and short stories.
The movie A Christmas Story has become a perennial favorite, largely because of its repetitive showing on cable TV. As I recognized when it first came out, it’s based on Jean Shepherd’s anecdotal short pieces that were based on his reminiscences (the stories were published in Playboy and other places). These were collected into two books, In God we Trust – All Others Pay Cash and Wanda Hickey’s Night of Golden Memories and Other Disasters
Those are certainly related books, though, being by the same author and about events in the same person’s (his own) life. The only reason one might not call one a “sequel” of the other is that the timespans of the two might overlap (I’m not certain if they do, but they might).
Wuthering Heights in Semaphore.
More seriously, the plot of Yojimbo was based ontwo novels by Dashiell Hammett. Unrelated, because they feature different characters. Also the two remakes of Yojimbo, A Fistful of Dollars and Last Man Standing.
Similarly, another film by Akira Kurasawa, Rashomon, is based on two unrelated short stories (not books – sorry) by Ryūnosuke Akutagawa. It gets its title and setting from his story “Rashomon”, but the bulk of the story from “In a Grove” (although Kurasawa actually added original material to the story).
As with Yojimbo, it was remade as a Western in the US – the oddball film The Outrage, with an appropriately outrageous cast – Laurence Harvey, Claire Bloom, William Shatner (as a preacher), Howard da Silva (Ben Franklin! as a prospector), Edward G. Robinson, and Paul Newman (with a moustache, as a Mexican bandit!)
And, of course, the film has been ripped off countless times by episodes of TV shows (although The Simpsons gets high credit for this exchange:
Marge: But you loved Rashomon!
Homer: That’s not the way I remember it!