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 Hidden Prince of Oz
The publication of the book was timed to coincide with the centennial of the original Oz book, "The Wonderful Wizard of Oz" (as was also true of Edward Einhorn's "Paradox in Oz" and Dave Hardenbrook's "The Unknown Witches of Oz"). It was the winner of the Club's Centennial book contest, which received over 100 entries in 1998.