After John R. Neill's death in 1943, the Oz series came to a stop. It was revived by Jack Snow, a fervent admirer and collector of L. Frank Baum's work, and author of The Magical Mimics in Oz (1946), and The Shaggy Man of Oz (1949). In these two Oz titles, Snow ignored any incidents occurring after Glinda of Oz, and worked only with characters created by Baum or himself. I enjoy these stories, but these are the first to be illustrated by someone other than Neill, and the combination of new author as well as new illustrator make them feel a little odd to me. Frank Kramer was a friend of Snow's, and he was in the unenviable position of replacing Neill, who had illustrated the last 35 books!
Who's Who in Oz is a bit of an Oz oddity - This book from 1954 is an alphabetical listing of over 600 Oz characters, from the 39 books then in print. Plot summaries of each title are also given, as well as biogaphical sketches of authors and illustrators from the series. The dust jacket for this books takes its image from the endpapers of The Royal Book of Oz, and I think is an inspired choice.