Recently the United States ISBN Agency (Bowker) began assigning ISBNs with the prefix 979. Unfortunately, some industry infrastructure has not been updated accordingly, and as a result some of our Print-on-Demand partners have been unable to properly process these ISBNs. As this is a new standard, we expect updates to be made quickly, but if you sign up your project with a 979 ISBN, there may be delays in your title being listed with external partners, like Amazon.
BookBaby is only issuing ISBNs with the 978 prefixes, not the problematic 979 prefixes.
On BookBaby's end, we are well prepared and the BookBaby Bookshop has no problem with 979 ISBNs. Your title can be made available there immediately, where you'll also gain all the advantages of Bookshop - larger royalties and more details about your audience!