R.R.
Good for you knowing each and every car seat has an expiration date which is listed somewhere on the car seat. The car seat expiration is based on the date of manufacture not the date of purchase or beginning of use. Most car seats expire in 5 years some in 6.
Car seats can become unsafe when they expire and the reason why car seats are given an expiration date and it is not just to get your money. The car seat does become damaged in ways you may not see. The plastic shell degrades and warps due to the changing conditions, the harness begins to wear and the Styrofoam can degrade. All of these things make your child less and less safe.
Graco says on their heart-to-heart blog website that they imprint “DO NOT use this car seat after Month, Year” on the bottom of every car seat.
http://blog.gracobaby.com/2010/02/11/car-seats-have-expir...