This also fails to take into account that ISBNs also contain the publisher ID in them. So identical copies of a book could have different ISBNs depending on which markets they are sold in.
However, within the block publishers can assign ISBNs to different imprints.
The ISBN always indicates the country it's from, the United States getting the biggest block, other European nations and Japan getting their own, with Africa, the Middle East, and so forth all getting a block in common.
See https://en.wikipedia.org/wiki/List_of_ISBN_registration_grou...