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..
Copyright status of The Wizard of Oz and related works in the United States
The McGraws co-wrote another Oz book, "The Forbidden Fountain of Oz", which was published in 1980. Its copyright lasts for seventy years after the death of last living author. Lauren McGraw is still alive, so "The Forbidden Fountain of Oz" will enter the public domain seventy years after her death. Since it will remain copyrighted until at least 2085, it will be the last deutero-canonical work to enter the public domain.