When I wrote that, I was thinking about (1) high rep sets, and (2) short rest periods, so mainly about metabolite accumulation.

When we use reps in reserve, we obviously perform one or two fewer stimulating reps per set, and we need to take that into account when calculating the number of stimulating reps for that muscle in that workout. I think multiple sets to failure can work, but my preference is to work with 1 or 2 reps in reserve and do a couple of extra sets. I just find that the long-term progressive overload is easier that way.