I'm confused, it sounds like you're saying the same tape was being ejected every week and then reinserted without any rotation. But in that case, shouldn't the weekly backup process have failed because the tape was full? Was nobody getting those alerts?

Or do you mean the backup process was fine, but they restored from the wrong media, a very old tape that was about to be overwritten, instead of retrieving the one with last-week's copy?

I read it as they were saying the manual part of the process never happened, so the backup from the first week was just sitting ejected forever and they had no alarming to notify them that the new backup failed to write to tape.

no, the first Sunday night after the backup process completed. It ejected the tape. It sat there for years until someone realized they needed to restore from the most recent backup. Since a new tape was never inserted, the backup was from years ago.

What happened afterwards? Was that manager still at the company, at that time?