Back before those prequels and EU books screwed everything up in the continuity, I always saw Yoda as being a native of Dagobah, not an exile there. Like a Buddhist monk or something that a fledgling warrior had to track down in order to be worthy of training, he trained Jedi like you'd teach Zen -- not via some stupid "code." If you look at the OOT without the filter of the EU or the Prequels, Vader never even met Yoda, let alone knew where he was, because Obi-Wan discovered and trained him instead, thinking he could do just as good a job as Yoda. According to the ROTJ novelization, only the Emperor had heard of Yoda, and was the one who figured out that he completed Luke's training after Ben's death.

The O-OT universe is a sensible place, where 12-year-olds aren't elected as rulers of a planet, where Zen warriors don't have a rulebook, where small children aren't trained in the art of battle, and where you don't die in childbirth from a broken heart.