fading is cutting off food a predeterminate time before harvest to let the plants use up the nutes they already have available, which will cause them to consume some or all of their own lower leaves to feed bud growth.
this does nothing to remove any nutrients from the buds. in fact, it does the opposite, as the plants response to the stress will be to cause as much reproductive growth as possible.
plants don't absorb nutrients in the form you pour them in your pots, they absorb ions of those nutrients that are freed up as the nutrients break down in your grow medium.
most of those ions are permanently bonded to the sites they are used to build. permanently.
the ones that are "mobile" are mostly stored in the root system, where they can be distributed to the rest of the plant, and the leaves, where they are used as catalyst in the photosynthesis process.
flushing is pouring a large amount of water through your grow medium to remove built up salts from fertilizers. again, this does nothing to your buds, the effect is almost identical to fading, just happens faster.
so efforts to remove nutrients from buds are useless, and in fact, cause the plants to move as much material to the buds as possible in a last ditch effort to reproduce before they die.
this is science. this is from botany 101. for real. you can look it up easily.
i realize Doctor Who said pretty much the same thing, several times, just above, but i thought maybe someone else saying it might help you see it, and forget the bro science you have accepted as real