One thing I notice is that you have the three books in a "Standard" collection folder. Instead they might be better in a "Collection SET" folder, or separate each Book Collection into its own Standard Collection of images.
I can only assume your standard collection called "Book Collections" has images in it that are not in a book. So I do not think there is a problem with numbers.
My Collection SET folder does not show any images at all-
and my workflow for book creation is to delete a standard collection of images once I have saved the book design as a "Book Collection".
However keeping the images within a 'Standard Collection' may be of benefit if you have sorted the images and want to keep the sort for a slide-show. The 'Book Collection' may have the images on pages in a different sort order.