Yes, I figured out that setting the delimiter (and other things) in each text file is the way to go.
But I’ve made no progress on the repeated cards.
Oops. Yes, I have! Thank you. Your point to check the note type got me straightened out.
It seem the new import processing was getting a different note type, so it re-added the notes with the different note type.
My bad. I had made a special note type for this deck, but was actually using another note type (they’re all the same except for the name). For some reason, all the previous import dialog processing guessed/defaulted to the other note type, so I was blithely bopping along unawares.
But the new import processing is doing that differently (probably better/more correctly). Kewl.