Makeup Expiration Date


So I just learned that makeup has an expiration date (not that I didn't "know" that makeup eventually got gross and old but I never thought about it.) I'm less concerned with stuff like primer, foundation, concealer, and even mascara because I use these products everyday and they eventually run out. What I am concerned about it my extensive eyeshadow collection that has grown in the past year. I have at least 20 palettes (I know it's a problem) and I can't possibly wear them all the time, especially in the time it says they expire. Also kinda concerned with my lipsticks because I have a handful of limited edition Kylie cosmetics ones that I don't wear every day too. I'm sure I've used the same eyeshadow for years and never had a problem before but now that I have so many, I'm concerned that they're going to go bad and that I wasted my money. I think most of them say 12 months on the back but I'm wondering how long I actually have with them? What's the longest you guys have kept and used eye shadow and lipsticks and even makeup in general?