Once a print-edition book (i.e. a paperback or hardcover) is published to Amazon, it cannot be removed, even if the book has been unpublished or retired. This is because of Amazon's used book market which allows booksellers to resell books in perpetuity. Because there is no such thing as a used eBook market, your eBook edition can be removed from Amazon. If you have an old version of your print-edition book still displaying on Amazon and would like to direct readers to your new edition, contact your Author Manager and we can have Amazon add a link to the old detail page that will redirect readers to the new detail page.
If your print-edition book has been unpublished or retired and is still showing available for sale through Amazon itself (i.e. not a third party seller), Amazon may have had inventory on hand prior to the unpublish/retire date and will continue to show availability until these books sell through. Alternatively, Amazon may mistakenly believe they have inventory on hand and will correct the availability status when a copy is ordered by a customer and they realize they do not have any inventory.