Why Must Read Level 3A - Theory Book: Piano Adventures?

I bought this book to have ready when my daughter finished the 2B book. We recently started it, only to discover that it is missing about 10 pages in the middle, which appear to have been replaced by pages from a Disney song book instead. (In the photo it goes from page 8 to page 5, from Morning by Grieg to Part of Your World from The Little Mermaid.) It is followed by a few more Disney songs before picking up theory again at page 17. We are now outside the return period so I guess we’re stuck with it.