Jokers Can Not be Used as a Single Tiles or in a Pair  (Article ID 46)

Abstract:   Under no circumstance can a Joker be used in place of a single tile or a pair. 

Question from a player:  Can I use a joker in a pair of as a single tile? 
 
Answer from the NMJL:   “At no time can a Joker be used for a single tile or in a pair.  A Joker or Jokers may be used to replace any tile or tiles (a symbol tile is not necessary) in a Pung, Kong, Quint or Sextet.”

Source:  Mah Jongg Made Easy (2020 page 23, #10, page 30 para. 6)

Other answers from the NMJL:

 “Joker or jokers can never be used for a single tile, or for a pair.” 
 
“At no time can a joker be used for a single tile, in an answer or in a pair.  Joker may be used to replace any tile or tiles in a pung, kong, or quint.”
 
“… A joker cannot be used for the single or pair tiles.  A pung is three like tiles, a kong… four like tiles.  In an exposed hand you may call a discarded tile and expose the kongs as example.  Jokers may be used in the kongs but [tiles] in a grouping of four singletons … can only be called to complete a sequence on a declaration of mah jongg.”  
 
Source for other answers:   National Mah Jongg League Bulletin Q&A (1975 page 3, 1986 page 5, 1990 page 13) https://www.nationalmahjonggleague.org