The booklist has been put together by volunteers on a rolling basis - that is, nobody sat down and worked for eight hours straight on creating a comprehensive list of The Best and Most Important History Books. As such, each section generally represents someone with a specific area of expertise contributing the works that they can best judge, and as a result, yes, there are holes.

If you (or anyone else) has expertise in China during WWII and can contribute both titles and reviews of relevant books - as you can see, we include a snippet from a professional review with each book in that section - we'd love it if you/they sent them to us via modmail for inclusion.

To add to /u/mimicofmodes' comment, we also have an East Asia booklist, and although it does not contain WWII books at the moment, we are working towards a major update which will likely include some on China in WWII. In the meantime, if I may make a direct recommendation, Hans van de Ven's China at War: Triumph and Tragedy in the Emergence of the New China 1937-1952 is quite a good overview of the Second Sino-Japanese War, Chinese Civil War and Korean War.