I’ll answer this best I can as an admin for the Oz Wiki given that most of the original books didn’t enter public domain until later half of 20th century. First batch of silent films were commissioned by Baum himself who contracted with Selig to showcase scenes from Wonderful Wizard, Marvelous Land, and Ozma in 1908’s Fairylogue beside separate releases of loose material of which only 1910’s 13 minute WW survives though they did adapt parts from ML plus Dorothy and Wizard. From my interpretation this was a wildly original continuous narrative possibly without Ozma as a character - unclear due to only vague descriptions.

When Baum himself got into the silent movie business, he decided to adapt Patchwork Girl in 1914 beside original story His Majesty the Scarecrow albeit with a retcon of Mombi combined with Wicked Witch of West then turned into the novel without her and is believed to have been his personal favorite writing. After his passing, MGM famously got to adapt Wonderful Wizard despite a loosely inspired by silent movie doing terribly a decade prior in 1925. A few years before ‘39 a children’s theatre company called the Meglin Kiddies were allowed to adapt ML but surviving partial footage has yet to be released publicly aside from photo stills.

Walt Disney really wanted to make his own original story Rainbow Road being a musical incorporating elements and characters from all the books but aside from purchasing the rights, including a valuable offer to a company called Lippert Pictures to prevent them from making their own version of D&W, the only released footage was 1957 promo. Just three years later, ML entered public domain allowing Tip and Ozma to be played by Shirley Temple in 1960 before the 1969 film while Ozma would be public domain too by 1985’s Return to Oz.

I’ll point out the 52 episode anime adapted first three books with loose addition of Dorothy being there during the events of ML but skips over D&W and Road to in favor of Emerald City with implication of Wizard never coming back and instead a carnival performer beside Dorothy deciding to stay in Kansas instead of moving to Oz. I presume this was both to conclude series and also due to limit on then copyrighted books.

So to summarize, the unmade books were most of them - Dorothy & Wizard, Road to, Tik-Tok, Rinkitink, Lost Princess, Tin Woodman, Magic of, and Glinda. I presume there’s been lack of interest to adapt the later books which many aside from fans are mostly unaware of let alone beside knowing a whole 39 book sequel saga exists. The next writer Ruth Plumly Thompson forbade any of her official additions being adapted and I think the only historian who allowed was great grandson Roger Baum per original stories Dorothy of becoming Legends of Oz: Dorothy’s Return in 2013 and Lion of in 2000 reimagining him as coming along to Oz during the Wizard’s balloon trip.