From the diary: "January 4, 1981
"I have been reading The Patchwork Girl of Oz and I'm anxious to get back to it plus I have to go to bed soon so I'm making this short -- okay?"
I'd guess I was trying to read L. Frank Baum's books in order. When the two Trot & Cap'n Bill adventures didn't sell Baum returned to writing Oz books. The Patchwork Girl of Oz was the first of those. He continued the Oz series with one book a year until his death.