If I had to guess it would be something such as concatenating a bar code. In UK, we have items which when reduced all they do is add the new price to the end o

If I had to guess it would be something such as concatenating a bar code. In UK, we have items which when reduced all they do is add the new price to the end of the bar code. ie. If some product is barcode of 3035555074225 and it's then reduced in price, the reduction including some checksum is added. So, if the new price of 3035555074225 is 50p, the code becomes 303555507422500502 (Where we add 0050 for the price, and 2 is the checksum). Next time you are in the supermarket just look at the barcode and you'll spot the pattern. So for your example, maybe there was some EPOS system that the guy had inside understanding of how barcodes worked on coupons and could easily pair them.