As of the end of Towers of Midnight do we know who added the extra wards to Callandor that were present when Jahar Narishma collected it for Rand in The Path of Daggers?
(The retrieval happened off screen, between chapters 14 and 21)
The dialog between Rand and Jahar is (written from Rand's point of view):
Rand snatched the bundle before Narishma could proffer it. “Did anyone see you?” he demanded. “What took you so long? I expected you last night!”
“It took a while to figure out what I had to do,” Narishma replied in a flat voice. “You didn’t tell me everything. You nearly killed me.”
That was ridiculous. Rand had told him everything he needed to know. He was sure of it. There was no point to trusting the man as far as he had, only to have him die and ruin everything. Carefully he tucked the bundle beneath his cot. His hands trembled with the urge to strip the wrappings away, to make sure they held what Narishma had been sent for. The man would not have dared return if they did not. “Get yourself into a proper coat before you join the others,” he said. “And Narishma... ” Rand straightened, fixing the other man with a steady gaze. “You tell anyone about this, and I will kill you.”
The Path of Daggers, Chapter 21 - "Answering the Summons"