The plant uses what it needs and expels the rest . And in the "test" the plant with no flush was preferred in the taste test . Even flushed weed once green still contains chlorophyll. As someone mentioned when he flushes in hydro the ppms of the solution raises in the last weeks of life eventhough the plant still drinks water .
How do you suggest the plant "expels the rest"
Three ways to control the way a plant acts.
One is light spectra/intensity/timing.
Training or cutting to manipulate auxin.
The other is root-zone EC.
The plant will always draw in water first, followed by nutrition.
If your EC varies, it effects the plant.
If too low, the plant will draw in too much water, and become water logged.
Too high EC, and the plant will draw in too much nutrition and leaf tip burn.
Extremely high EC will desicste the plant by reverse osmosis ( the plant burns because it's nutrient/water solution is drawn out into the soil/media )
It can adjust the amount of sugars in its roots, to adjust the amount it draws ( by osmosis ) but only in increment of less than 100ec per day
The net elemental profile is up to uou, though.
If your plant needs more potassium say, but you are over feeding nitrogen, it will just draw in too much nitrogen.
The plant doesn't take up just what it needs in the ratio it requires, osmosis just draws in the net elemental profile you supply it.
That is why some gardeners have a better skill, because they are able to observe and tweak the liquor to what a plant requires, and keep their plants fed to her requirements, without producing imbalance/lockouts.
Or some plants are easier growing, because they are not so susceptible to malnutrition.
Can you suggest by what method does the plant expel unneeded nutrition?
Do you think it shits it back out?
Chlorophyll is very much like blood in animals.
It is produced by the plant itself.
It is not excess nutrition in solution in the plant.