If a player claims a discard for mah jongg and the player's mah jongg was in error, the claimed discard remains with that player's dead hand and cannot be reclaimed or called by another player.
Players should verify a winner's mah jongg before throwing in their hands. If the mah jongg was not verified, and a player throws in their hand and breaks the wall, they are responsible for stopping the game.
If a player picks a tile from the wall, declares mah jongg, and starts to expose his tiles only to find out he did not have mah jongg, their hand would be considered dead.