Did some more searching for lastname, firstname sorting and I found this post from the very helpful DetlevD and it works.
T=4
F=ARTISTSORT
1=(.) (.)
2=$2, $1
3=0
I noticed it did not have the backslash character '</b>' so I'm figuring my earlier troubles have something to do with how the delimiting character is set in my Mp3tag settings.
Edit Indeed that was the problem. I have semicolon set as the delimiting character (tagging FLAC for squeezebox server and would like AC/DC to stay AC/DC) in Mp3tag. I replaced the backslashes with semicolons in the other expressions and they now also sort to lastname, firstname.