@Mr Stillwater,
This is not about the 9 vs 13 digits.
isbn's puchased from a lot of 10 or less have the numerical digits laid our differently than from a lot of 100 or more.
This makes it obvious to a reveiwer that this title is self published with no major marketing or publicity.
Therefore, they will not review the book.
These isbn's also prevent the book from being listed in "Books in Print"