Stickers got bigger with the 2002 expirations - 4¼ x 3½ inches.   The month number inserts were laser printed, and there were several different fonts used.

A bar code, the word PASS (or PASSED), and some vehicle information (make, model, year, VIN) was also printed on the month insert.
These elements could use different fonts and be in different positions depending on where and how the insert was printed.

Starting with the 2008 stickers, the base sticker itself was also bar coded.

Seen on eBay.
I contacted the seller, and asked if the sticker was really gray.   They said it was !!!