A tile is called for Mah Jongg and the hand is exposed and discovered to be Mah Jongg in error. Is the called tile 'dead' or can another player call it?

The tile is part of the dead hand and cannot be called by another player EXCEPT when the tile had been called for Mah Jongg by two players simultaneously, and the player next in turn has called Mah Jongg in error. In this case, the tile can be claimed by the second player who declared Mah Jongg.