Question: Someone discarded a tile and misnamed it. However, they had the correct tile in their hand. What happens in this situation?

Answer: A player cannot replace the discard with the correct tile from their hand. Instead, it should be brought to the player’s attention and then the tile should be correctly named. Any player can rename it. Once a tile is named or hits the table, it is down. 

Sources:  Mah Jongg Made Easy, page 19, #17 ( states tiles must be “fully named”), National Mah Jongg League Bulletin Q&A 2020 (states “named” and does not use the word “fully.”