Even if there are enough copies of a title available in your school's collection when you create an assignment, those copies may expire before your assignment start date. For example, if the title is metered by checkouts, your school may run out of checkouts before your start date.
If this happens, the email address(es) you opted to notify when you created the assignment will receive an email explaining that more copies are needed. This email will include a link to purchase more copies of the title.
You can also visit the Title assignments page (under the Admin tab in Marketplace) and filter the calendar to see all assignments that need more copies.
If more copies are not purchased 7 days past the assignment start date, the assignment will be canceled. This will be noted on the assignments calendar, and a notification email will be sent to the email address(es) you entered when you created your assignment.