I don't think that's necessarily the case, I think if you've got at least a decent 3 part, or something, that you can transition it a few different ways, it's just got to be done gradually, and with some foresight, planning. But certainly both ways are fine, if done with care. I think that's where measuring the EC and whatnot comes into things, it determines the next step to take.
But I have to admit, I don't take daily measurements, I do check ec as I mix it, especially the custom parts, but I don't always check what's coming out of the plant, unless I see something wrong, and I keep a standard mixture that's good for all stages, it's just the concentration, and what's done to it beforehand...
Lately, I've been giving a lot of my K+ with a spray bottle, and creating a bit of C02, I belive. It works extremely well.
2 KHCO3 → K2CO3 + CO2 + H2O. and prevent PM while I"m doing it.