Titles, editions and ISBN
A title in two editions is two products, and selling last year's edition to a student is a return and a complaint. Keeping edition and ISBN as part of the item means the invoice records exactly what was supplied and the stock figure is meaningful. The ISBN also makes the item scannable, which matters when a customer arrives with a list of fifteen books.
Selling a syllabus as a set
Most academic sales are a set for a class rather than a single title, and building that bill one line at a time is slow with a queue behind. Keeping the components as separate items and billing them together gives an accurate stock figure while producing one clean invoice — and it shows you which titles in a set run short first, which is the reorder signal.
School and institution accounts
Schools and coaching institutes buy in bulk against an order and pay on an invoice, sometimes weeks later. Those accounts need a referenced bill, a delivery record and a statement, because they are settled on paperwork. They are also the accounts where a shop carries the largest balances, so a credit limit set in advance is worth having.
The number to watch
Unsold stock at the end of the academic season, by title. Books are returnable to some publishers and dead to others, and knowing which titles did not move while returns are still possible is worth real money. The movement report answers it in minutes; a shop working from memory finds out when the next edition arrives.