Thanks for the replies. This response kind of is for both, as there is repeat info there.
I did look at the page both referenced at http://help.mp3tag.de/main_tags.html and see that both are listed. Assuming that I can infer M4A from iTunes in that table, the two fields in question do not have an entry under iTunes.
I use Extended View for most everything, the panel is not even on my view.
The two fields I mention work fine in MP3 containers, but I am finding that they do not in M4A containers, mine being AAC encoded.
It is rare that I see these fields in M4A containers, but they are in some files that I get. I can say that dbPowerAmp, just simply using the explorer extension from it, I can see and edit these fields without any problems. I really do not have other software, tagging specific, to try as MP3Tag is my goto for all.
I guess I will download some other software and see how it works there. This may have been an issue for me all along, I just looked for those tags today as I was told they were there. I will check some older files too.