A new character, the female elf warrior Tauriel, who does not appear in Tolkien's fantasy novel, turned up in the second Hobbit movie and is back in "The Hobbit: The Battle of the Five Armies".
The character played by Canadian Evangeline Lilly was created to give young girls a way into the overwhelmingly male-dominated plot, director Peter Jackson and screenwriter Philippa Boyens told Reuters.
"Now they'll know how to kill Orcs," Jackson joked in a joint interview with Boyens after the London world premiere.
"We have probably committed atrocities with the canon," said Boyens, who with Fran Walsh won an Oscar for best adapted screenplay for the last movie in "The Lord of the Rings" series, based on the trilogy Tolkien wrote after "The Hobbit".
She was responding to criticism from "Tolkien scholars", as well as reports that Tolkien's son Christopher, who edited his father's posthumously-published "The Silmarillion", the only one of Tolkien's Middle-earth fantasy books that has not been filmed, dislikes the movies.
"But there's two things to be said to that, really. One is we've brought an awful lot of people to these books and now they get to explore that.
"And second, Professor Tolkien himself said that he had created this mythology and he hoped other minds would come to it, because it's a myth, it's a living, breathing thing."
It may be a living myth, or perhaps a fire-breathing one, which is what the Benedict Cumberbatch-voiced dragon Smaug brings to the films, but Jackson sees little chance of making more Middle-earth movies beyond a director's "extended-cut".