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..
March Laumer
March began writing his Oz books in 1962 (one year before the publication of the fortieth and last "official" Oz book, "Merry Go Round in Oz"). He was a frequent correspondent of Ruth Plumly Thompson until her death in 1976. Most of Laumer's books were published by his own small press, Opium Books, in Hong Kong, or Vanitas Press in Lund, Sweden, often with illustrations by Lau Shiu Fan. Laumer's books often make drastic changes to the series and involve adult themes that have led some fans to label them pornography based on some oblique and non-negative references to bestiality and pederasty in "The Green Dolphin of Oz" (1978), his best known and most widely circulated book, as well as the first to be published. Many of his manuscripts were works in progress for many years, and some of them may have been discarded.