Calling a Discard for a Joker Exchange (Article ID 121)
Abstract: Discarded tiles cannot be called for use in a joker exchange. Joker exchanges are done only when a player picks a natural tile that is in an exposure or already has the natural tile in their rack. This ruling is not found in Mah Jongg Made Easy.
Question from a player: I had an exposure of three 6 Dots and a Joker. Someone threw a 6 Dot. Can I call the 6 Dot and take the Joker?
Answer from the NMJL: No, once the 6 Dot is discarded, it is a “dead” tile. A tile many never be called to replace a Joker in an existing exposure.
Source: NMJL Bulletin Q&A 2021
Other answers from the NMJL:
“A tile may only be called in order to make an exposure or for mah jongg. It may never be called in order to replace a joker in an existing exposure.”
“A discarded tile can only be called for an exposure or mah jongg. You may not use it to redeem a joker in an exposure.”
Other sources: NMJL Bulletin Q&A (2020, 2012, 2011, 2010, 2009, 2008, 2003) https://www.nationalmahjonggleague.org