clandestine institutional knowledge - The phenomenon in which everybody knows the documentation is wrong and people are so pissed off at said documentation that they don't ever bother to try to fix it. Instead new hires have to play Indiana Jones to find the two people left in the organization who have any working knowledge of the thing and beg to be trained up so they can actually do their jobs. Normally, the newly trained individual doesn't bother to update the documentation, either.
footnote: Most of the time, nobody has the access to update the documentation anymore, which is why nobody ever bothers to fix it.