I know that each edition of a book should have its own ISBN. My understanding is that if a second printing corrects a few typographical errors, that doesn't generate a new edition that needs a new ISBN, but making editorial changes such as adding or removing material does. What about something like a coupon or an offer? Here's my situation: I have a book that's about ready to go to press. In the body of the book I discuss some products, and there is a possibility that the manufacturer of one of the products I mention might be willing to work with me to provide a discount code for readers of my book. The company has expressed some interest, but so far they haven't come through with the discount code. I have waited several weeks already, and I'd like to get this book out so I can clear the decks to move on to the next project. Let's say I go ahead and publish the book, in print, Kindle, and EPUB editions. If this company subsequently provides me a discount code, can I add a last page to the book (after the "About The Author" page) with the discount code and a brief blurb about the product, without triggering a need for a new batch of ISBNs? This new page will be basically advertising, not part of the subject matter of the book, so I'm inclined to think it may be okay. But ... does anyone know for sure?
That doesn't actually change the content of the book in any meaningful way, so yes, you can just add it.