Thanks for the question, Andrew. All products should be shown on the main price book page, in either the “Prices” section or the “Inherited prices” section. Those shown in the “Prices” section are taking a price directly from this price book, and those in the inherited section are getting their price from the parent price book.
If you’d like to add a set price for a product on this price book, find it in the list (either in the “Prices” or “Inherited prices” section) and click the right-most button to set a price for it manually. See the Setting explicit prices section of the above guide.
To help you find a product on the page, you can use the Ctrl + F keyboard shortcut to search product names (or Cmd + F on a Mac).
I hope this answers your question, but please let us know if you still need help. Thank you!