Question: Can I call a tile if I am playing a Singles and Pairs hand or a grouping such as NEWS, FF or individual tiles such as 123?

Answer:  No, but there is an exception to this rule, read on. You can never call to expose a single tile, single grouping or a pair during the game. However, there is an exception. If the tile discarded tile is the one needed to complete Mah Jongg you may call it to complete a single tile, a single grouping or a pair. As well, all hands under the Singles and Pairs category are concealed hands, and therefore can never be exposed during the game, unless the discarded tile is needed to complete Mah Jongg.

Source: Mah Jongg Made Easy 2024 page 14 para, THE PLAY