Is this natural or man made?

SADs are much harder (perhaps impossible) to securely erase, you’re right

“A couple” is sometimes not enough, but a few more is considered secure enough for most contexts, though gov will often physically shred the disks to be sure.

I only know for sure with macOS, but I image isn’t this applies to all: the OS has a built in secure erase feature that will overwrite a whole disk enough times to be confident that the data is irrecoverable