On Day 40 I posted about the requirements for assigning digital ISBNs. The information I uncovered is still correct and true, but the information I found was not compulsory as I first believed.
I indicated that different file formats require different ISBNs. That is, an .EPUB file would be assigned a different ISBN to a .MOBI file. To assign multiple ISBNs for each type is advised by different companies, but is merely a suggestion and not an absolute. You can, if you choose, assign the same ISBN to ALL digital formats, whether it is an .EPUB, .MOBI, .PDF or even some of the other ones. If it’s in digital format, you can use one ISBN. This is unlike print copies, where paperback and hardback are supposed to have different ISBNs.
After much deliberation, I’ve decided to use a single ISBN for all digital formats. There is a risk that the digital publishing industry will change which means I might have to assign a different ISBN later, but there are two advantages for me presently:
1. Fewer ISBNs mean fewer potential mistakes. I have a spreadsheet where I list my printed ISBN (assigned to me via CreateSpace) and also my digital ISBN. More ISBNs mean more potential for muddling them up.
2. It’s cheaper. ISBNs cost money, and even though it’s not a great deal when buying in a block of 10, (around $8 each), they do add up. Since I’ll have to assign an ISBN to every digital book I list separately for sale, if I release a book in three different digital formats (EPUB, MOBI, PDF), that chews up three ISBNs to no great advantage.
Readers don’t care if ISBNs aren’t consecutive in a title. Only those in the publishing industry or in related fields would notice. As long as the numbers are accurate in the library/bookseller catalogue, who cares?