"Also no good if the tapes are worn out because you cycle around the same five daily backup tapes for 5 years."
Some years ago, I got a call from one of clients to go visit one of their satellite offices to check up on their backups. The non-techy person in charge of the tapes had been correctly following the instructions of placing the correct tape in the drive before leaving each day and then removing the ejected tape and putting it on the shelf. Except they'd not had a backup even start for over 6 months because the tapes had expired and were being ejected as soon as 8pm backup process started.
I can't remember why they asked me to go in the first place or how they found out there might be a problem, but the upshot was they suddenly decided it would be a good idea to use the backup apps ability to email a status report to head office after each run. I heard later they sent a full new set of tapes to every satellite office because none of them had been completing for many months.
Note, this was an insurance company, many years ago, DOS clients and Netware servers were still al the rage.