I'm not familiar with Korzybski's theory of truth.

I'm only familiar with it through Hayakawa. The reference you provided to support your claim that the General Semantics theory of language is "defunct" says this about the GS theory of truth:

Hayakawa is quoted as saying:

[General semantics] tells you what to do and what to observe in order to bring the thing defined or its effects within the range of one’s experience.

which the ELL entry precisifies as:

The literal meaning of a statement expressed by sentence Σ is given by defining the method for observationally verifying the conditions under which Σ is properly used.

All of which sounds pretty close to Davidson and Tarski to me, though I'm not an expert. And not all that far from Yudkowsky.

I made my comment mentioning Language in Thought and Action before reading your post. I now see that your point was to fit Eliezer into the mainstream of Anglophone philosophy. I agree; he fits pretty well. And in particular, I agree (and regret) that he has been strongly influenced, directly or indirectly, by W. V. O. Quine. I'm not sure why I decided to mention Hayakawa's book - since it (like the sequences) definitely is too lowbrow to be part of that mainstream. I didn't mean for my comment to be taken as disagreement with you. I only meant to contribute some of that scholarship that you are always talking about. My point is, simply speaking, that if you are curious about where Eliezer 'stole' his ideas, you will find more of them in Hayakawa than in Peirce.