Did you list your unused NEMA adapter for sale? I was similarly frustrated when I bought in 2019 because the 14-50 (and 6-50) adapter was out of stock for a long period of time.My 2 cents. Most buyers are probably like me. Never used the NEMA adapter. Also never used the hitch that also came with it. Why have customers pay (remember nothing is free) for these if a lot of them will never use them?
I have a feeling that most who have them and don't use them STILL want to hold on to them just in case they're helpful someday.