And yes, car seats expire.
I had no clue about that until I wasted $20 for a convertible car seat at a garage sale.

I ran home so excited for my excellent purchase! I got online, googled my car seat hoping to see how much money I saved, but I couldn't find any recent ones online. I went to myDiaperSwappers car seat forum and asked around. Then I learned about how Graco bought the company Century (my used seat) in 1998 and my car seat is expired.
Expired? What does that mean anyway?
Turns out all carseats expire 6 years after they are made. This is to protect people from overusing them past safety standards. It also helps people purchase newer seats as safety standards change each year.
Every car seat has a stamp of their manufacturing date and also states when it should cease being used.
Josh wanted me to go back to the garage sale and inform the lady that she sold me an illegal car seat and politely ask for my money back. But I just didn't think this was proper garage sale etiquette. Even if she did sell it to me in ignorance it isn't the seller's responsibility to refund money if the buyer isn't happy....not at garage sales! They sell their stuff super cheap cause they don't want it/can't use it anymore and want to give it away basically.
So now I have a mostly useless carseat. I certainly refuse to use it in my car - instead I am going to leave it inside the house and let Lizzie play with it. So far she thinks this is a fantastic idea! Saturday she buckled herself in while I was folding clothes in front of her and she fell asleep inside her new seat. After smiling at the cute moment, I unbuckled her and reclined the seat against the couch (she is the lightest sleeper in the world, and once awake won't go back to sleep....so I refuse to mess with her when she finally does nap) She woke up happy and refreshed!