It really isn't.
If I remember right, they said the emails were “lost” about 2 years ago. I’ve been in IT for 25 years and I’ve never seen anyone with a backup rotation that long. Typically, it’s only 3 months, then the media is overwritten... be it tape or disk, it’s simply not feasible to keep backups that long, especially data in the massive volumes we are talking in this case. In the case of magnetic tape, they don’t even have a stable shelf life that long