Here is a great collector’s reference for Wizard of Oz books: Bibliographia Oziana published by the Wizard of Oz Club, copyright 1976, this a 2002 printing of the revised and expanded edition, originally published in 1988. Authors are by Hanff, Greene, Martin, Greene, and Haff, softcover, 146 pages.
Trust me, if you want to collect Oz books, you will like this book. Describes the different editions and states (printings) of all the major Oz books by Baum, Thompson and others. Also includes some odd rare editions, and many photographs of covers. This book gives you all the nitpicky details so you know what you’re actually looking at and can make wise buying decisions.