flushing before harvest is an ego-stroke based on zero evidence. The reasoning that used to be given changed in the last 5 years because studies showed flushing does absolutely nothing to mineral content of the flower. Now, it's conveniently soem other magical reason that also has zero evidence to support it. Nobody in the science community bothered to test it before because the plant does not have an excretion system, so the hypotheses was incredibly flawed and unlikley from the get-go, given existing knowledge of plant biology.
Burden of proof lies on the person making the statement. This hypothesis about flushing at end of harvest has never been proven.
You can never disprove things. That is logically impossible. This is not what scientific research does. You can show that specific attributed relationships or correlations exist or very likely do not exist. Otherwise, all you get is snake oil salesmen with lots of promises but never put in the effort to prove any of it. "That" is anecodote, lol.
Avoiding buildup in the plant does not require a flush. You simply don't feed it more than it is using. There are a lot more options out there than starvation. If it was important, then every single outdoor crop ever was/is trash, because good luck flusing the earth, lol.
Also, flower is not evolved to store things. they are sex organs. They don't do a whole lot of photosynthesis, either, so worrying about light hitting the buds is yet another unproven hypotehsis that is often repeated but nobody bothered to prove it. If you knew flower had 1/100th of the chlorophyl as the top layers of leaves, you'd know that too is a very unlikely relationship to worry about. Cell diferentiation matters. Organs have specific functions.
If a plant has a rootzone problem or you have allowed a buildup of nutes in the soil that provide a toxic level of nutrients over time to the plant, then it's a good time to flush. Otherwise, there is no cause to any effect as to why you'd want to flush. that is the only thing it can do -- dilute what is in the substrate and that is only necessary if you gave too much in the first place.
blind taste tests have also shown people have no fucking clue which buds were flushed and which were not, lol.
Surprisingly, I agree more often with the "1x1=2" guy below, lol. Kinda scares me a bit. (just kidding around). As long as the canopy is strong enough and you dodn't kill all the leaves before it finishes, all is fine. Sometimes it's nice to be lazy that last week or two. I stop adding nutes to my reservoir on fill ups the last week, but that is purely to save myself some time and only if my canopy can still provide those nutrients. If it is draining the leaves, it's clearly still using those nutes to build various molecules in the plant.. to grow... to ripen.. No matter is ever lost or gained in the universe.. the atoms have to balance out at both ends of the equation.
Just to reinforce.. the plant has no excretion system. There is no such thing as flushing a plant. It physically cannot work like that. Impossible. As far as toxicites, you should be reacting to any buildup long before a 'fix' requires something as stressful as a flush of the substrate. Even if you flush it, the plant still has to use up what it has taken in before the toxicity symptoms abate. Also, no gaurantee you overfed all of the nutrient molecules... if only 1 is building up to toxic levels in the plant, and you leach out all other nutes from the substrate, now you have a boatload of deficiencies starting to develop, lol....