You use one number at a time. The rest of the numbers can be used for future publications. These could take four to six weeks, so plan ahead of time in order to avoid delays in production. Rush service is available but that means extra money. Don't get me wrong.
Some people are more comfortable working with a book's ISBN than the title.
In other words, without the ISBN, no bookstore will stock you book. Paul Chika Emekwulu - Not necessarily. It depends on a lot of factors. Hardbound books for example cost more. Paul Chika Emekwulu - Yes, absolutely.