I worked for an MSP a million years ago and we had a customer that thought they had lost everything. They had backup tapes but the backup server itself had died, after showing them the 'catalog tape' operation, and keeping their fingers crossed for a few hours, they bought me many beers.
I always had the Customer keep a written log of which tapes were used on which days. It helped for accountability but also prevented the "Oh, shit, we have to catalog all the tapes because the log of which tapes were used on which day are on the now-failed server."
