Well, I think technically powder items can go bad, but they are unlikely to if they are stored carefully (kept away from sunlight & moisture, kept at an even room temp). They should last you years and years.
I finally just finished my original Vex e/s from 1997, and it seemed just fine. I just kept it stored in my traincase. I think you should be fine with stuff only a few years old.
As long as it's brand new it should last a good while. It's not like mascara or foundation. If an e/s is used however I would be more careful: bacteria on skin==> applicator==> eyeshadow.