The packages of many consumer goods, including toys, have individual production codes stamped on them . These are not printed, but machine stamped on the packaging at the time the goods are produced and packaged. The codes are visible as a colorless indentation. They are used by the manufacturer for the purposes of quality control to identify things like the date on which the item was produced, in what factory it was produced, and out of which production batch it came.

The Simpsons toys have begun showing these code stamps on the back or bottom of their packaging. You can interpret the codes to find out on what date an item was produced. If your toy package has a code stamp of A1122, this refers to the 122nd day of the year 2001. The second digit is the last digit of the year, and the last three digits represent the day of the year. With these codes you can tell how long it took your toy to get from the assembly line into your hands. In-demand toys produced in countries like China usually arrive in stores anywhere from a couple weeks to two and a half months after production depending on the pick-up and shipping methods used by the manufacturer and retailer.

You can also look at these codes to determine which variations if any of a toy were produced later or earlier. However, this method may be less accurate for packaging variations than for toy variations. Packaging may be printed up well in advance of the manufacture of the toy, so the order in which the packaging is put onto the assembly line may not match the order in which it was printed at all. The toys themselves are more likely to be packaged immediately after they are produced, at which time the codes are stamped on the packaging.