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ID47-North (Player 4) Forgot to Take Their 13th Tile
Question: We are in the middle of the Charleston and North (player 4) realizes they forgot to take their 13th tile. Can they go ahead and take their 13th tile?
Answer: Yes, they can pick their thirteenth tile but, only before the Charleston or before East has discarded their first tile.
Source: Mah Jongg Made Easy 2020 page 19 #9