Ok so from what I understood, this visualisation displays all the ISBNs that are assigned into countries, then across publishers. Books that are not highlighted are the ones that are not present on Annas Archives? Is that so?
Annas Archive has both books in their archive, but they also have other datasets that connect a book ISBN to the metadata (title, author, publisher, ...).
In my visualisation https://isbnviz.pages.dev you can see which books they actually have the files of (blue) and which ones they know exist because they have the metadata from some other source (like google books, ...) (red). Finally, there are also ISBNs not contained in any of the sets that Annas Archive has, and these are either assigned or not assigned. A lot of the 979 prefixed ISBNs are not assigned, that means, no country/publisher has the right to assign them to a book. Other ISBNs are assigned to a publisher, but they just haven't published a book with that ISBN yet. Or they may have published a book, but Anna's archive doesnt know about the book because its not in their (or the ones they scraped) dataset.
Also what do you mean by unassigned?