yellow leaves don't mean anythign other than a deficiency in the plant. Flush, relative to end of harvest SOP, is 99% likely to be an urban myth after just a modicum of research done on it.
trichomes
pistils
density...
use those three physical characteristics... only flush when the plant has a toxicity so bad it requires such a serious response. rely on cause and effect, not anecdotal magic.
it's a great example to warn of the very likely possibility a lot of stuff thought up by isolated growers with small samples and no attempt to compare to a control group is totally bat-shit crazy and unfounded.
if you think a nute is too high in concentration, go ahead and feed less or water-only for an irrigation or ?? until the problem abates.