[juanez]

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The instant cards hit the muck, they're dead.


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Straight from Roberts Rules:
Cards thrown into the muck may be ruled dead. However, a hand that is clearly identifiable may be retrieved at management's discretion if doing so is in the best interest of the game.

The key word in the rule is MAY. It just depends on the situation. The key word in your post is INSTANT, which is just a bad rule if that's the rule where you play.

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Even if player can correctly identify or name both cards, the hand is dead.

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Just naming what the hand was doesn't make it "identifiable". I interpret this rule to mean that the cards haven't been totally mixed into the muck in such a manner as to make it impossible to distinguish which ones they are. This is exactly why a dealer should never place cards on top of the muck or let mucked cards linger on the table - any discarded cards should immediately be swept into the muck so they cannot be considered retrievable and there can be no dispute later.