Well said. The devil is in the details for how one goes about doing this process step, particularly since most people don't even 'try' their backup until there's been a real problem.
I think I've seen that happen a few years ago; can't recall the reasons why...might have had to do with the TM disk going to capacity?
Somewhat similarly, I've found my NAS on two occasions to have gone "dead" with similarly no particular notice or warning, even though it was configured to send an 'SOS' email. The first time appears to have been a disk corruption which somehow mucked up the (Linux) OS that caused it to hang but not shut down (nor complain). The second time was a disk failure, as even a replacement of the drive's controller board didn't restore it to life. Given how underwhelming this NAS has been from a reliability standpoint, I don't think I'm going to keep it around as part of my future data integrity plans, nor replace it with another NAS ... perhaps I'll bring back up online my old PowerMac G5 running Tiger Server.
-hh