@ZodWallop: IIRC, the ePub spec thingy requires you to identify the source of the page numbers (e.g., via ISBN-13).
(I may be entirely dreaming that up, because why the hell would the ePub specs start making sense?

).
EDIT:
https://www.w3.org/publishing/epub3/...c-nav-pagelist
So, yup, the ePub specs continue being mind-boggling.