One thing a friend of mine (hi Adrian!) did at my old workplace, that I found incredibly annoying at the time, but later realised was exactly the right thing to do, was set up a wiki for us to use and then refuse to answer any question or acknowledge any information except via that wiki. After a while I just gave in and before telling him about anything, stuck it on the wiki. Years later when I left, every time anyone asked me a question I could honestly answer "it's on the wiki."
People love to hate on Bezos (less here than elsewhere, though, I guess) but this is exactly the tack he used to convert Amazon's IT setup to services, and I think both were shrewd moves.
I've never seen or heard of a team that keeps documentation for their complex algorithms. It's just not done.
And if it was, I'd bet that they get out of date very fast