Incorrigibility is way too strong an assertion, but there's a sense in which I cannot be completely wrong about my values, since I'm the only source of information about them; except perhaps to the extent that you can infer them from my fellow human beings, and to that extent humanity as a whole cannot be completely mistaken about its values.

I suspect there may be an analogy with Donaldson's observation that if you think penguins are tiny burrowing insects that live in the Sahara, you're not so much mistaken about penguins as not talking about them at all. However, I can't completely make this analogy work.