Reprinted with permission from the Atari 2600 Connection Newsletter:

Investigating the Dates on Cartridge ROMs

by John Earney

In Scott Stilphen's "Collecting Atari Cartridges" article in issue 23, he writes: "Many carts have numbers or letters stamped onto the end labels. It's possible that certain production facilities used these, but for what reason?" I didn't get this information from Atari or anything, but I do know what the numbers mean. The number indicates when the cart was manufactured. There are three digits in the number. The last digit indicates what year the cart was manufactured and the first two digits indicate what week of that year the cart was made. For example: a cart has "453" stamped on it. So this cart was made in the 45th week of 1983.

Notice that the first two digits can't be greater than 52. Since the summer of 1991, when I first came up with this theory about the numbers being a date, I haven't found a single cart whose first two digits were greater than 52. Also you can compare the earliest date on a particular game's carts to the catalog that the game first appeared in. Based on all that evidence (and a bit more stated below) I think my theory is correct. Sometimes there is an "E" before the number and sometimes there is an "R" or a "D" after the number. I don't know what those letters indicate. My guess is that they indicate which production facility made the cart. Anyone know?

Actually if you don't mind opening things up, you can find out when just about anything in your collection was made. Most integrated circuits (ICs) have their date of manufacture printed on top (integrated circuits are those flat black rectangular components that you'll find on most circuit boards.) The date that's printed on ICs is always a four digit number and it usually is by itself (although sometimes there's a few letters before or after the numbers.) The last two digits indicate which year it was made and the first two digits indicate which week of that year it was made. 7935 would mean the 35th week of 1979. It may take a bit of practice before you can spot the date because there's typically a lot of writing on ICs. Here -- I'll bust open a Combat cartridge as an example.
OK - here's what's written on the IC:

(c)1978 ATARI

This particular IC (a ROM in this case) was manufactured during the 41st week of 1981. Keep in mind that the final product would have been made after this. The number printed on the end label for this cart was 202, so it took 31 weeks for them to get the ROM put into a cartridge. That's quite a bit longer than usual--they must have ordered a huge amount of Combat ROMs back in 1981!

CAUTION: Sometimes the part number for the IC might look like a date. The part number for the Combat I opened was C011201-01. That doesn't look much like a date, but there is a common family of logic gates whose part numbers look like 74xx. You may see some ICs that say 7404, 7400, 7414, or some other 74xx number. That doesn't mean they were made in 1974!

You should expect to find an IC in any electronic equipment that has to do some amount of "thinking." For example, a joystick or paddle won't have an IC because they're just switches, but there will be one in a cart or game console.
OK, now back to Scott's cool article about label variations I have a bunch of label variations to add, but there's way too many to list here. I've been compiling a huge list of label variations for 2600 games for about a year now.

AtariAge - 2600 ROM dates