So when someone who has been stilled/gentled is healed by someone of the same gender, they are only healed to 1/3rd of their original power. If, after being healed to 1/3rd of their original power, they are stilled/gentled again and then healed by a member of opposite sex, can they recover 100% of their original power?
From the mouth of Robert Jordan himself, "RAFO", for those unsure what this means, read and find out, was Jordan's response to questions that were either spoilers or he himself had not yet decided.
Siuan and Leane being stilled again and Healed by a male to full strength...
"RAFO, because I might decide to use that as a plot device!" (That got a few chuckles).
Number 13 So we know Jordan thought about this, however, he died before ever confirming what would happen.
This quote leads me to believe though, that it would be possible to heal someone again, and to full power, he was just debating actually using this in the plot or not.
Also Number 10 Confirms OP's claim that healing done by the opposite gender is required for 100% healing.
For Alys Kinch, the Healing of stilling must be done by the other gender to be fully effective. A woman Healing a woman or a man Healing a man results in less than full restoration. It all ties into that theme I keep harping on. Men and women have to work together to be their most effective. And while the weave used by Flinn for Healing is not exactly that used by Nynaeve, either would use the same weave on a man or a woman.
In The Wheel of Time Companion, we finally get a canon-answer to healing being 100% effective, rather than just the interview quotes or educated guesses we were previously left with. (Interview quotes from Jordan were sometimes subject to change).
Under the entry for Logain Ablar:
Logain was accidentally Healed by Nynaeve; the rebel Aes Sedai held him prisioner while they decided whether or not they could afford to gentle him again, give Rand and his amnesty. Since Leane and Siuan were not as strong as they once were after being Healed, the rebel Aes Sedai assumed that Logain wasn't either; none of them knew that this Healing needed the opposite sex for completeness. In fact, because he had been Healed by a woman, he was just as strong as ever.
We also see that Damer Flinn healed three Aes Sedai that were stilled at Dumai Wells, and they didn't seem to be any worse for the wear.
We are never given any evidence that anything special happens when gentling/stilling someone that's already been Healed of the same affliction.
It never happens in the books, so Jordan's "RAFO" meant that we actually "find out" nothing. We can only assume that:
- They'll be healed to their original power levels, as it'd be like taking a poorly-fit bandage and putting a proper one on
- They'll only be healed to their post-Healing levels, as the first healing capped them
Unless additional materials are published, we'll never know. The Companion was the last major addition to The Wheel of Time planned, and Robert Jordan is no longer with us to give Word of God answer.