How to create a book from multiple collections?

You can show all the photos together from multiple collections as suggested by Ian, but I find I always lose my Custom Sort this way.

Try this-

1. Create a new (empty) Collection (call it "New Collection")

2. Select the "new Collection" (the screen will be blank)

3. Immediately set the new Collection Sort Order to "Custom" (even though it does not contain photos)

4. Now select one of your 'organized' collections, [Ctrl+A] to select all, and drag images onto the "New Collection"

5. Repeat Step-4  for each or your organized collections in the order you want (Chapters?)

With this method I did achieve ONE collection sorted as wanted.

Use this "New Collection" to go to the Book Module and photos will be sorted on the filmstrip as per the "New Collection"

***Immediately click the tab to {Create a Saved Book}- this "Book" Collection will be the collection you work with every time you want to edit the Book.

You can select two or more collections in the 'Collections' panel by holding down the Cmd (Mac) /Ctrl (Windows) key while clicking on the collection name.