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.
Mah Jongg In Error with a Verbal Declaration of Mah Jongg and no Exposures (Article ID 52)
If a player declares mah jongg but has not exposed any of their tiles, they may change their minds and continue playing without penalty.
Mah Jongg In Error with a Tossed in Hand That Destroyed the Wall Scenario 4 (Article ID 54)
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.
Mah Jongg In Error by Two Players and Another Tossed in Their Hand (Article ID 56)
In a rare occasion, when two players declare mah jongg in error and another player has tossed in their hand