"not expounded" is correct and usable in written English.
You can use it to indicate that something has not been explained, clarified, or otherwise described in detail. Example: The deeper implications of the text were left unaddressed and not expounded upon further.
Yet, doctrines are not expounded, for this is a book of the songs of Israel that describe the way Yahweh was experienced and worshipped.
Further, its relationship to manufacturing processes is not expounded.
It was just this sliver of life that you see that's not expounded upon because it's not her story.
However, the relationship between self-reported health status and QOL is not expounded in the model; in particular, it is not clear how self-reported health status relates to other life domains relevant to QOL.
What he did not expound on is that the Mets do not necessarily see Reyes as the prototypical leadoff hitter.
He would not expound on his reasons for leaving Notre Dame -- he called it a personal decision and said he was grateful for his two seasons there.
While she did not expound on those consequences, she suggested that the pressure put on the Iraqi government would be tied to a "phased redeployment" of American troops out of the country beginning this year.
McCarthy is not expounding any particular end-of-the-world scenario (though it sounds to me most like a nuclear holocaust), but tapping into our collective psyche, into a deep-seated, suppressed fear of what may lie beneath once the fragile veneer of civilisation is torn violently away.
However, our result does not expound the other cases in [9], Theorem 4(b).
He does not expound on what people are victims of, or who or what caused this state of "victimization".
