YES AND NO
Current assignments for YES and NO are:
DAH - Yes
DEH - (Low elven) Yeah? Right? Won't you?
NAH - N0
NEH - (Low elven) Isn't it?
We see here that there is basically one word meaning yes and one word meaning no. However, as certain groups of elves have moved through the generations we have examples of some shifts in language. We can call this shift "low elven" and is probably more provincial sounding than the original. We have this in English such as when some people use the word AIN'T instead of ISN'T ("isn't" being a contraction and signals a shift, already, from more formal speech patterns).
While some people choose not to use this word it does not affect their ability to understand it.
We can see Treestump use this lower form of elven with the Djun's hounds when he says something and concludes it with "deh?".
I have some other theories involved with the specific usage of these words but wanted to hear some feedback from other fans. Am I "shooting with a well-strung bow" now?