Yea, I wouldn't rely on HD on a shelf. Source: I've had hundreds of hard drives over the years. Some that are 1 year old and dead, after sitting on a shelf. Some are 20 years old and still work (kind of a test at this point to see how long they'll still spin up).

There's a reason 3-3-3 backup is the guideline. From my own experience, you need data on no less than 3 different storages, not including the production data.

I've had situations where 2 of my Backups didn't work for some reason, either media failed, or data wasn't backed up though it was supposed to be, etc. That 3rd has saved me many times.