Copyright status of The Wizard of Oz and related works in the United States
"The Wonderful Wizard of Oz" was published in 1900, and was the first to enter the public domain in "1956". This allowed Reilly & Lee, the publisher of all the other Oz books (as well as Baum's other books) to issue their own edition of "The Wizard of Oz", which had previously been published by George M. Hill Company and later by the Bobbs Merill Company after Hill went bankrupt..
The Enchanted Island of Oz
The Enchanted Island of Oz is a children's novel written by Ruth Plumly Thompson and illustrated by Dick Martin, and first published in 1976. As its title indicates, the book is an entry in the series of Oz books created by L. Frank Baum and his successors. It is the last (and shortest) of Thompson's 21 novels about the Land of Oz.