Expiration date on new flares

[steplift20]

I was going to buy flares for my gun cause all of mine are expired,when I looked at the new ones at Walmart they say they expire 2020 ,that's only two years ,I thought they should be a lot longer than that, so what I'm asking is if you buy new flares how long should they be before they expire? I'm thinking they could have been on there shelve along time, what do you guys know about them