Earlier quoted context omitted.
Can't find it now, but I've often seen a phrase to the effect of "If you don't regularly test that you can restore from backups, then you don't actually have backups", and it seems to ring quite true here.
It's up there with "unless you test power supply failover, don't rely on that generator to save you". I know of one case where power failed, the "24 hour" generators kicked in, power company says "We'll need 12 hours" and the outage happened 6 hours later when they ran out of oil.
When I was there this didn't go too well and they couldn't get one their data centres online again - failover to their other centres did work though. This was ~20 years ago in the finance sector.