You got it right. You use that approach on multi-joint movements. On most isolation exercises the minimal weight progression is too high relative to the weight you can use on your sets to properly use double our triple progression. Unless you have fractional plates.
Sure, although they might not progress at the same rate. So, using the triple progression model itās possible to eventually have 1-2 lifts in one rep target zone (e.g. 6 reps) and 1-2 in a different one (e.g. 4 reps) because one/some stalls faster than others.
The purpose of triple progression, which is based on double progression, is to get continuous progress for as long as possible. You basically āmilkā a training zone for all itās worth, you change only when there is absolutely zero progression, to spark new progress.