Following L. Frank Baum's death in 1919, other authors continued adding novels to the series. Official additions to the Oz legend remained very popular through the 1920s, 1930s, and 1940s. The Bromberg collection contains a complete set of these books by the following authors:

John R. Neill

• The wonder city of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1940.
• The scalawagons of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1941.
• Lucky Bucky in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1942.

Jack Snow

• The magical mimics in Oz. ill. by Frank Kramer. Chicago: Reilly & Lee, 1946.
• The shaggy man of Oz. ill. by Frank Kramer. Chicago: Reilly & Lee, 1949.

Ruth Plumly Thompson

• Purple prince of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1922.
• Cowardly lion of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1923.
• Grampa in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1924.
• Lost King of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1925.
• Hungry tiger of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1926.
• Gnome king of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1927.
• Giant horse of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1928.
• Jack Pumpkinhead of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1929.
• Yellow knight of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1930.
• Pirates in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1931.
• Ojo in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1933.
• Speedy in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1934.
• Wishing horse of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1935.
• Captain Salt in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1936.
• Handy Mandy in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1937.
• King Kojo. ill. by Marge. Philadelphia: David McKay, 1938.
• Silver princess in Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1938.
• Ozoplaning with the Wizard of Oz. ill. by John R. Neill. Chicago: Reilly & Lee, 1939.

The collection is also rich in modern continuations and retellings of the Oz stories. The following authors are represented in the collection with over a hundred editions: Donald Abbott, Kenneth Gage Baum, Roger S. Baum, Bill Campbell and Irwin Terry, Rachel R. Cosgrove, Edward Einhorn, March Laumer, Gregory Maguire, Eloise Jarvis McGraw, Hugh Pendexter, Eric Shanower, Sherwood Smith, Gilbert M. Sprague, Alexander Melentyevich Volkov, Gina Wickwar, and Marv Wolfman, among others.