Originally Posted by kovidgoyal
The problem with that concept is that passing epubcheck doesn't guarantee anything at all, other than that the file will pass epubcheck.
You can spend decades studying astronomy, but it doesn't mean you'll be able to guarantee with complete certainty that the sun will come up tomorrow.
It guarantees it's free of the errors for which epubcheck checks. Any problems with epubcheck are largely problems with the standard itself (though I'm sure it has some real bugs still).
It would simply be silly not
to demand that epubs pass epubcheck if you're in the business of commissioning documents that will be archived.