Since most problems are 99.9% user error, I assume that was my problem in the Kindle Converter not converting the epub after I changed the code, even while EpubCheck validated it... KC might be a stickler with certain aspects of the code, and a little boo-boo in the wrong place could make it choke.
Out of curiosity, Tex, were the ebooks you bought that used ISBN for UUID epubs or an Amazon flavor? (If Amazon, that proves I did something wrong, imo.)
As to ISBN entry, I read that in
this PDF from ISBN org, for entering info in metadata. This is also where I read the <Publisher> s/b the top level publisher, and if the book is published under an imprint, then <imprint> should
also be present. This made sense since the portion of the ISBN that identifies the publisher only identifies the top level publisher, not its imprints.
However, I could not add dc:imprint to the metadata and have it turn out right. That is, once I converted with KC it showed my top level publisher as the publisher, and didn't even parse the imprint metadata at all, as seen in the conversion log.
About that time (yesterday afternoon) I started wondering if this PDF does not relate to epub metadata, but metadata entered on the Bowker site when registering ISBNs to a title, hence the name of the PDF.
Which would mean you can enter the ISBN with hyphens in epub meta and I don't need to add "dc:imprint" ... though that last one is more a worry since the ISBN 'won't match the imprint,' so ... it does seem like both s/b present .. ?
EDIT: I keep saying "Kindle Converter" but it's called Kindle Previewer.