In addition to the Nervous Frat Boy encounter where he says he was U16, last year there was also the Counter-Party Plan encounter, where Chuck said He was U15:
He inhales a hissing breath. "Fucking Utgard. It's the key to some puzzle, I fucking know it."
He pulls a plastic bracelet out of his pocket, like the one's hospitals give to the patients wealthy enough to go there. "U15" is printed on it in large, block letters.
"The people who ran the hospital we were all in, they were part of some Project Utgard. That's what the U stands for. And apparently they're funding Emily's party." He breathes noisily again.
"I mean, maybe it's above board… maybe they're just trying to make amends or whatever. I don't buy it, though."
I asked Kinak about this and he said:
Poor Chuck, in a quantum state between U15 and U16, the time when someone who could collapse his state vector long gone.
Go ahead and update the wiki so they're both U15. It's either that or he's collecting bracelets.
So whoever U17 is, s/he isn't Chuck.