But some of "it" has been handed down through the teacher-student interaction. This by itself doesn't guarantee quality or fidelity of the material passed (to say the least) but you do know the provenance.
Personally I would have liked to see something like academic peer reviewed evaluation applied on the inherited "it" but I am not holding my breath. If you bring fresh "it" from the outside the system however, well - then the burden of proof is on you.
There is no fresh "it" - it all comes from recognizable sources, and Dan has said that himself in the past.
It's also not from outside the system - unless you artificially limit the system to a particular politically organized structure.