Black Gate expresses misgivings about the decision to make 'The Hobbit' into a trilogy of films: Three Hobbit Films for the LOTR Fans = Trouble. Apparently there are copyright issues that prevent the filmmakers from mining additional story content from any Tolkien work other than the LOTR appendices (in addition to The Hobbit novel itself of course). But this still leaves the filmmakers with a lot to work with, since the appendices contain a chronology of backstory events not described or referenced in The Hobbit but that transpire simultaneous to the events described in the novel. For example, if I remember correctly, Gandalf's temporary absence prior to the dwarves' arrival at Rivendell is explained in the chronology by his attendance at a meeting of the White Council (which Galadriel, Elrond, Saruman, and presumably the other three wizards/istari also attended). The Hobbit film teasers show a face-to-face encounter between Gandalf and Galadriel, and since Galadriel is entirely absent from the novel, we can infer that this is one backstory item that has been lifted from the chronology and inserted into The Hobbit films to flesh-out the story and lend the films the same continuity with the LOTR films that Tolkien himself worked into his later books after The Hobbit was published with no apparent intention to turn the children's novel into the prologue of an epic work of mythopoetic fiction.