If they're bought together, like mine were, and they have close serials, they've be almost identical; if you then run them in a ZFS mirror like I was, they'll receive identical "load" as well.

Since mine had ~43000 hours, they didn't fail prematurely, they just aged out, and since they appear to have been built pretty well, they both aged out at the same time. Annoying for a ZFS mirror, but indicates good quality control in my opinion.