Toshiba failure x2

[Vulcan]

can anyone explain to me why a hard drive, if left un-powered and untouched for an extended amount of time, will become operational again for a short amount of time?

Explain? No. That would require a definite diagnosis, which would likely need the drive in expert hands. As labtech said:

can never tell accurately until a thorough analysis is complete on each.

I've seen that behaviour before on a few drives, and I could guess at a couple of possibilities based on experience with other drives (and I'm sure the experts here have many more "war stories" with this behaviour than I do), but guesses aren't the explanation which you're asking for. This is the whole reason I didn't reply to that part of your previous posting - I'd be wasting my time (and yours too) with guesses, as you've already said you're looking for an explanation, and are sceptical of what you're told.

If this detail is important to you, then IMHO you'll have to pay for hands-on diagnosis from a good DR company for whichever drive(s) you choose (even if you don't want the data e.g. from the donor drive). There are limits to remote diagnosis, even with a crystal ball - but that's just my view