Although we would like to have every book on Small Demons indexed, we still have a long way to go. There are several steps we go through with each book, with the first being the collection of the book's basic information (title, author, cover, description, etc.).
For books by publishers we have agreements with, we're then able to process them with a combination of automated and manual efforts to determine what people, places, and things are mentioned in them and include the surrounding passage.
If you see a book's page that doesn't show the people, places, and things mentioned in the book it's likely because the book was mentioned in another book so added only as a reference so far and we have yet to process it in full.