To the OP, my daughter was born in 2/04 and her infant carseat (which I used for my son, then gave to my neighbor) expires in 12/09. We bought it in 2004, but it was manufactured in 2003 and the expiration date stamped on the bottom is 12/09. It's also a Graco Snugride.
FWIW, we're trying for a 3rd kid and while I hoped I could still use the same seat (till I checked the date), I noticed that the newer ones are much, much nicer. The padding is much thicker, many of them have side impact head protection, plus they almsot all accomodate larger babies than the 2004 seats did. My SIL just got a new one for her 3rd kid and it goes to 30 lbs/30 inches. I know ours was 20 lbs/26 inches. So if you have a fast grower, the newer seats will get more use.
And to Fintastic, I would just go out and buy a new seat. It wouldn't even be an issue. Believe me, my husband is incredibly, hmm, thrifty, and might try to make the same case, but there is no way I would be stopped from buying a new carseat. Just think about if you get in an accident and something happens-you'd never forgive yourself and probably hold a lot of hostile/resentful feelings towards your husband. It's not worth it. I know they're not cheap, but the risk is too much for me to handle. And really, my husband paid such little attention to our carseats that I can almost guarantee that if I bought a new one in a similar design, he'd never notice. Not that you want to be deceitful, just sayin'....