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Let's say I'm one away from an iipeiko, having a 2, 3, 4 and a 2, 3 in the same suit. This needs to be concealed to get the point, but it shows up in someone's discard and I ron it while in richii. Even though it's the winning tile, does that still ruin the point for the iipeiko? This is just one example, so would it work the same for everything, either always ruining the point for it's concealed or always awarding the point due to it being the winning tile?

When you ron with a concealed hand (riichi or not), the last set in open but the hand as a whole is still concealed.
Some yaku needs the hand* to be concealed, some other yaku need only the sets to be concealed.

* I should say "the tenpai hand" to be exact.

For examples:
Iipeikou requires to have a concealed hand, so you can finish it by ron.
- This hand scores iipeikou:
concealed: - - -
melded: ron
The hand is concealed, so iipeikou is valid.

- That hand does NOT give iipeikou:
concealed: - - - tsumo
melded:
The double run is concealed, but not the hand. So no iipeikou here.


Sanankou requires concealed triplets.
- This hand worth sanankou:
concealed: - - -
melded: - ron
The three triplets are concealed, so we have sanankou.

- That one does NOT:
concealed: - - -
melded: ron
The hand is concealed, but have only two concealed triplets.

Thanks. I didn't know that it was talking about the whole hand being concealed for the iipeiko, or that ron wouldn't make it open.