Hey welcome Cookie Monster!

How many covers have been in rotation? If you've been using them daily for a year, I think I'd be pretty pleased with that? I tend to wash my nappy stuff in cold/cooler water because heat's not great for elastic (like constant tumble drying isn't great for nappies, underwear, socks - the elastic wears out more quickly).
They won't last forever though...I mean...think about a pair of your daughters pants or a pair of your underwear being worn and washed that often.

If you haven't used them that much though...then yeah it would be strange for them not to have lasted. I guess I'd need to know how often they've been used and washed - do you think that the elastic going is reasonable wear and tear?