You never chowed, punged or konged.
You never claimed a tile from another player’s discard. No chow, no pung, no kong taken off the table. The hand is built from your own draws.
You may still finish it by taking the winning tile from a discard. A concealed kong DOES break it: Hong Kong counts a kong as breaking concealment however the tiles were acquired, unlike the Japanese game.
Staying concealed costs speed and buys faan, so it is a read on the table rather than on your tiles. Early, with a shape that is already close, passing on a claim is usually right. Once an opponent shows two or three exposed sets, finishing first matters far more.
Believing the winning tile must be self-drawn. It need not be. You can stay concealed all hand and still win on a discard. If you also drew it yourself, you score Self Draw as well, which is a separate row.
With Self Draw it makes the familiar two faan of a fully concealed win. It layers onto shape and suit patterns without conflict. Concealed with four chows is two faan. Concealed in one suit with honours is one plus three, so four.
Does a concealed kong break it?
Yes. Hong Kong counts any declared kong as breaking concealment, even one built from four tiles you drew yourself. The Japanese game keeps it concealed; ours does not.
Can I win on a discard and stay concealed?
Yes. The final tile may come from a discard. It is every earlier set that must be unclaimed.
Is this the same as a fully concealed hand?
Not quite. A fully concealed win is this plus Self Draw, counted as two rows of one faan rather than one larger row.
Play Mahjong Winds
Every win shows its faan line by line, using the table on this page.