After L. Frank Baum’s first two Oz novels, nearly all those stories are structured around the preservation of and return to the status quo. Ozma remains in charge of the Emerald City. Some kids get to go home, others find a home in that city, and still others (especially in Ruth Plumly Thompson’s sequels) are restored to their rightful royal roles. That pattern’s surely a big part of the series’ appeal.
Books that make too great a change in that status quo are unpopular with fans. For example, most Oz fans dislike the way John R. Neill portrayed life in the Emerald City in the three books he wrote. Suddenly the houses become sentient, as Xamyul catalogues. Soon sentient cars roam the streets. Characters like Ojo, Kabumpo, and Sir Hokus don’t have the identities and homes that preceding books established. No later official Oz authors followed up on Neill’s stories, and the few examples of fanfiction that I’ve seen use some of his characters set his biggest changes aside.
The problem isn’t just consistency with the rest of the series, however. In fact, Baum was inconsistent on details large and small. He described characters dying in Oz and wrote that no one died in Oz, cut Oz off from the outside world and showed people traveling there with little trouble, said that magical artifacts could not travel to Kansas and depicted Dorothy encountering a magical artifact in Kansas. Oz fans don’t reject those contradictions; instead, spotting and if possible explaining them is part of the fun.
What makes Baum’s inconsistencies acceptable but Neill’s irksome? I suspect fans would accept the changes Neill made to the Emerald City more readily if his stories were any good. A talented fantasy illustrator, he didn’t have a good sense of character or narrative, nor good editors. As a result, it’s very hard to make any sort of emotional connection to Neill’s books and thus to become fond of them.
Edward Einhorn’s Paradox in Oz shows this rule in action from the other direction. It requires deep changes in our understanding of the Oz universe, with all versions of the myth existing in parallel. Yet I haven’t found any Oz fan expressing deep distaste for how that book changes Baum’s creation, probably because it’s a more enjoyable story.