Not just that but when ISBNs were first introduced, it was common thought that they were used for cash register price scanning rather than computer-controlled i

Not just that but when ISBNs were first introduced, it was common thought that they were used for cash register price scanning rather than computer-controlled inventory, so a number of early books had ISBNs re-used by publishers and it wasn't caught because they were meant to be the same price. These days you often see two barcodes on books, one is the ISBN and the other is the price.