Sometimes a story may not fit the desires for the printed book. Or, maybe there were story prompts that were left unanswered.  In either case, no problem, as the Purchaser or Editor you can ensure the book has only the right stories, and that those are in the right order.

Unanswered stories are not included in the book, so it's easy to ensure they are not printed. As the Purchaser or Editor, you will be able to see this when you preview the PDF before the book is printed.

Regarding submitted stories that shouldn't be part of the printed book, that is easy to regulate as well. As the Purchaser or and Editor, open up the edit story window for that particular story prompt. Simply uncheck the "Include in book" checkbox at the bottom of the window. That story will then be left out of the PDF and therefore left out of the book.