Every mahjong group has the same handful of arguments. They recur because the rules genuinely are silent or split on some of them, and because house conventions vary more than anyone admits. Here is where the actual rules land, and where you simply have to agree at the table.
Can you take a discard back?
No. Once the tile leaves your hand and hits the table, it is discarded. This one is not ambiguous, though it is the most attempted.
The related question, whether you can change your mind while the tile is still in your fingers, is usually resolved as: yes until it touches the table or you have named it, whichever comes first. Groups that play briskly tend to enforce the naming.
Two people call the same tile
A call to complete a winning hand beats a call for a pung or kong. That is the clear rule.
When two players both call for sets, the standard tiebreak is seating order: the player closest to the discarder's right takes it. Some groups instead give it to whoever spoke first, which is a recipe for argument and worth replacing with the seating rule.
Can you pass a joker in the Charleston?
In the Charleston proper, no. Jokers may not be passed during the standard passing sequence.
In the optional courtesy pass at the end, a joker may legally be included, since that pass is a mutually agreed swap. It is legal and almost always a mistake, since you are handing an opponent the most flexible tile in the game.
How many tiles should I have?
Thirteen, always, except in the moment between drawing and discarding when you hold fourteen. Exposed sets count toward your total: if you have exposed a pung, you hold ten in the rack plus those three.
Miscounting is one of the two most common causes of a dead hand, so the habit worth building is counting after every call rather than only when something feels wrong.
Do we have to play the current card?
Yes, if you want to play the standard game. The National Mah Jongg League issues a new card each April and the hands change, so an expired card describes hands that no longer count.
A group can of course agree to keep playing last year's card among themselves, and some do for a few weeks while waiting for cards to arrive. Just make sure everyone at the table is on the same one.
The meta-rule
For anything genuinely ambiguous, the answer is: agree before the hand, not during it. Mahjong rules disputes are rarely about the rules and almost always about two people having learned different house conventions and each assuming theirs is universal.
A new player asking 'how does your table handle this' at the start of a session is being courteous, not naive, and every experienced player knows it.
Put it into practice
Most rules arguments start mid-hand, when somebody is not sure what they are building and exposes something that does not fit. Our AI coach reads your actual tiles and names the direction before you commit, free and with no account.