At 50TB, they probably could have Just™ written three copies of the data to a pile of disks, sent one copy off to Iron Mountain, and kept the other two copies unplugged in a safe. I can understand the DIY solution might not be allowed for insurance reasons, but it's something so cheap they probably could have done both. Unless OSS was just taking them for a ride on storage, which... well, actually that seems pretty likely.
[0] To put it simply, there is no good medium for the archival of digital information. HDDs are not shelf-stable. Flash is even less shelf-stable than disk. Sony is actively trying to kill optical. LTO is shelf-stable, but good luck buying known-good or new drives for old formats. The only option is periodic cloning and verification of offline disks, or keeping all your disks online, which is the NAS solution.