Before we go too much further on the issue of asking to see a hand: i.e., under what conditions such request might be guaranteed vs. a privlege that can be denied, vs. when the cards are live or dead....
Please understand that the position of the TDA is set forth in Rule 17: a) if you ask to see you must have possession of your cards, or have tabled them; this doesn't guarantee you'll be granted your request, but if you have mucked face down you lose any such right or privilege. b) any caller of the last aggressive bet on the final street has an inalienable right to see the hand he called (on request), all other requests are at TDs discretion.
NOW, whether cards should be tapped to the muck, whether a hand is live or not, etc. is up to house policy. There just hasn't been enough blanket agreement at the past 2-3 Summits to adopt further language on the subject.
Conventionally, more often than not if the "presumed winner" asks to see any discarded hand, and the TD grants the request, that hand is live. But that isn't a TDA Rule per se. Also, more often than not, if a "loser" asks to see a hand not tabled, and the TD grants the request that hand is dead unless it's still in the possession of the player. But there are major TDA member venues that have different rules (all exposed cards at showdown are live, for example) so there is no TDA standard on these situations.