All of the fish that went in to QT with copper moved out after 30 days, and have been sitting in a holding tank while I figure out how to deal with the DT. The plan was to then take batches of fish through copper while the DT was fallow. The issue I ran in to was that, in order to go fallow for 76 days from where I was, I was going to have to deal with this over the holidays. Given the busy schedule, I decided to risk it and see if I could manage the DT until just after the New Year, and then go fallow.
I've seen no signs of any infestation in the DT since I removed the butterflies, which were all showing white spots. I have about 30 other fish in the DT, a collection of anthias, dwarf angels, wrasses, mandarins, and gobies, with a kole and a yellow tang, and none of those fish had shown any signs of infestation (no spots, no behavioral issues, etc).
I know this doesn't mean that I can skip the fallow period and just put the butterflies back in. But I did take it to mean that I could wait on dealing with the chore of maintaining what would amount to five systems over the holidays.
So for now, it's ich management in the DT (which, to be honest, hasn't really meant any change for me), maintain a tank of butterflies for the next month, and then pull the rest of the fish out of the DT and go through copper. I'm worried about how some of them will handle this, but more on that when I get there ...