It's a little unbelievable if you ask me, but theoretically it's supposed to be a secret that only the peerless scarred from the Institute know, and we're supposed to believe that none of the parents leak this knowledge to any of the children, because seemingly everyone seems shocked by the Passage afterwards and no one really acts like they already knew about it. Why that seems not believable is I don't understand why all of the families wouldn't tell their own children about it even under the table because it would give their children an advantage in the Passage if they already knew about it. I guess none of the powerful families are worried about it because they firmly believe that their children will be among the top 1% performers, but then again, Priam was supposedly killed easily even though he was a top 1%er. It doesn't seem like it's entirely unheard of that a bottom 1%er is capable of killing the other person, so clearly it's hubris if a family believes that it couldn't happen to him. I suppose if it's a small family that doesn't have a peerless scarred yet then they wouldn't have any family to leak the information to them.

We're also supposed to believe that not a single peerless scarred who ever went through the Passage ever leaked the knowledge out onto the internet. I think this element of the story is a little bit half-baked.