NO JOKER EXCHANGES AFTER DECLARING MAH JONGG (Article 60)

Commentary:  After a player claims a discard to declare mah jongg, they must use the discard as the winning tile. There are some situations where a player claims a discard to make an exposure then does a joker exchange with a natural tile in their hand that would then allow them to declare mah jongg.

Question from a player:  Can I declare mah jongg when my tile is discarded but need to do a joker exchange first? 
 
Answer from the NMJL:   You may not first exchange a symbol tile for a Joker and then use that Joker to call the last discard for either exposure or Mah Jongg.  You must make your “call” first.

Source:  Mah Jongg Made Easy (2024 page 23 #6)

Other answers from the NMJL:

“After mah jongg is declared there are no picks, discards, or exchanges for the joker.  A player can never declare mah jongg on a discard and then exchange the joker.”  
 
Source for other answers:  National Mah Jongg League Bulletin Q&A (1967 page 4, 1968 page 4, 1976 page 4, 1982 page 4, 1985, 1991 page 13)