What's Up With ISBN 978-1-56581-231-4 / 1-56581-231-X

Importing books from my shelves I scanned a book called The Sacred Cookbook whose back cover showed a barcode for ISBN 978-1-56581-231-4. LibraryThing matched that ISBN to The Black Coat: The Blackest Dye GN. When I manually added the book and set that ISBN, LibraryThing picked a cover showing a pink book with "World Wide Brands", probably matching January 2015 Issue (Universal Creativity Inc.). The book I have doesn't have an ISBN code printed on the reverse of the title page, but does list a publisher (Three Seed Productions) and publication date (October 2013).

I Googled that ISBN number and got results from dozens of seemingly unrelated books. Googling for the equivalent 10-digit ISBN code 1-56581-231-X got _The Black Coat: The Blackest Dye GN_ as the first hit, but also found some other books claiming to have the same ISBN. The 13-digit code search also turned up a couple open-source barcode generators which were using 978-1-56581-231-4 as what looked like test or example data.

So what's the deal with this ISBN code?
Is it a designated test or example code (in the way that example.com and example.org are domain names set aside for use in documentation)? If so, why do so many books use that code?
Is it a code meant for self-published works or something? If so, why haven't I been able to find a web page explaining that's what it's for?
Do stores that sell some of these books end up selling all of them for the same price? How do they manage inventory?

Some of those titles were miscombined on here, which I've now separated. The ISBN wouldn't be for self-published as they should have different numbers same as how publisher-publisheds have, if they have one at all. You might have hit on it with the barcode generator, if it's been mocked up using that number, but then left on unawares!

Unfortunately, Publishers sometimes reuse ISBN numbers. There's nothing out there stopping them from doing this. So what you've probably hit on is a reused ISBN.

Can i just say what a pleasure it is to see a thread title with a 22-digit number in it. If only every thread was so distinctively identified, the world would be a more accurate place.