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Changing an exposure during a player’s turn (Article ID 6)
Abstract: When a player calls a tile and places it on the flat part of their rack or exposes tiles from their rack, they are committed to taking that discard. They may add or take away from the exposure before discarding.
Question from a player: Can a player change their exposure before their discard?
Answer from the NMJL: A player may add to or take away from the exposure during his turn, as long as player has not discarded.
Source: Mah Jongg Made Easy (2020 page 15 para.2)
Other answers from the NMJL:
“If a player calls and exposes a pung or kong, she may add to it or take away from it (upon second thought) provided she has not discarded.”
“This player can make any changes to her exposure, as long as it is still her turn. It is still her turn until she discards, at which point no changes to the before mentioned exposure may be made.”
“You may add to the exposure or take away from the exposure as long as you have not discarded as yet. Once you discard, you are committed to that exposure.”
“Just as long as she has not discarded as yet, she may change her exposure by adding a tile or taking one away. Once you discard, you cannot change that exposure.”
“When a player calls for a discarded tile, makes an exposure of a pung, kong, or quint, that player cannot then decide that she does not want to make the exposure. The player has made the play by call and can only add to or take away from an exposure as long as she has not discarded.”
“Once a tile has been called for exposure and the exposure is put on top of the rack, the player may add to the exposure or take away from the exposure as long as the player has not discarded. But the player cannot decide that she did not want the tile she called for exposure, put the discard back on the table and the other tiles into her rack. A call for a tile is just like a pick from the wall. Once taken, it cannot be put back.”
Source for other answers: National Mah Jongg League Bulletin (1970 page 5, 1972 page 5, 1975 page 4, 1977 page 3, 1978 page 3, 1979 page 3, 1981 page 5, 1984, 1987 page 4, 1988 page 5, 1990 page 5, 1994 page 5, 1995 page 4, 1998 page 5, 2003, 2007, 2008, 2009, 2016, 2017, 2019) https://www.nationalmahjonggleague.org