One ISBN for multiple books sold separately

[Felix]

How should I add books that are sold separately but share one ISBN? Don't get me wrong this is not a collected edition or a boxed series or anything like that, but rather little books that are sent to retailers in a batch (with one ISBN) and then sold to the general reading public singularly. Thus I can buy a single book with ISBN x while there are several other (different) books out there with the same ISBN.

Is there a general policy regarding cases like this? If not, what do you suggest? Should I add them separately without the ISBN?

[Sandra]

Yes, Felix, you add them separately without the ISBN, and you put a librarian note so other librarians don't delete them in error. You can also put it in the description field.