I don\'t see how someone can use a Riichi Mahjong issue to handle a Chinese Official (aka MCR) problem. It\'s two separate rules with very different concerns, espacialy about the current matter.
Riichi and CO have two differnt definition for waiting patterns:
At CO, \"egde wait\", \"closed wait\" and \"single wait\" can be scored only if you wait for
only one kind of tile. (as you said)
At RM, the number of tiles you\'re waiting on
does not matter. You can choose on which wait you win.
For exemple, if you have this hand (concealed)

and win on the

:
- at RM you have to choose if you win by completing the 123, giving 2 points, or if you win by completing the 345, giving pinfu.
- at CO, you can
not get the point for winning on 123. Dot, end of the line.
It\'s two different concepts.
Any answer with one of them gives no info for the other one.
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To answer your CO question:
This problem have been treated long time ago on Mahjong News forum. The official book and is explanation file are obscure about this. If it occurs, you will have to ask the head-referee.
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@ silent observer :
If you can\'t claim a two-sided wait, what kind of wait can you claim?
Pinfu is not realy about \"having a two-side wait\", but rather \"having a no-point wait\". This case is certainly not a valuable wait, so pinfu will be scored.