I don't use the zoan cistern and don't care to discuss it.

Read Ilford's description of how VC papers work. I posted it earlier.

It passes green light. VC paper reacts to green light, graded does not.
That's why there's a difference in the way stained negatives print on
graded vs VC paper. You STILL don't understand, dammit! The light bulb
emits UV, and blue, green, yellow, and red light. The silver blocks
virtually ALL of this radiation, without favoring any part of the
spectrum. both VC paper and graded paper will provide similar prints
from all-silver negatives, provided the color of the light is adjusted
so that they can match.

In a yellowish-stained negative, the highlight areas have additional
density in blue light only. That is, the stain effectively blocks blue
light. Materials sensitive to bue light only will see this stain as
density. For such materials, the stain + silver density represents the
printing density, which is greater than the silver printing denisty
alone. But this means that to get the same contrast on graded papers
(blue-sensitive only) as you would with a non-staining developer, you
in effect have to 'underdevelop' the silver-only part. The printing
density of the silver alone would be insufficient without the stain.

When we use VC paper, however, we can get the use of only the silver
density. The contrast of the print on VC paper is lower, then, because
the VC paper is sensitive to green light, which the stain does not
block to any significant extent, and the silver-density part of the
negative is underdeveloped compared to a negative deevloped in a
non-staining developer. Instead of ADDING to the density of the
highlights, the stain might as well not even be there. This has nothing
to do, really, with the contrast-control function of the color filters.
It has ONLY to do with EFFECTIVE PRINTING DENSITY.

All this assumes we are using grades around 2 or 3 on graded paper, or
filters around 2 or 3 on the VC paper. If we place a high-contrast
(green-absorbing magenta) filter (filter 5 or so) in the light path,
the density of the stain will come somewhat into play, and will reveal
some printing density. The trrouble is that the gradient in the lower
tones and the highlights may not match, leading to problems in
printing. It will NEVER match the contrast of a grade 2 or 3 overall.

NOW DO YOU UNDERSTAND??????????????????????

The bleach Michael referred to does not remove the stain, only the
silver. I have done this part of the experiment without using an alkali
bath. That bleach is Farmer's reducer. You can use it either mixed
together, or sequentially to remove the silver.

I have an old 35 mm camera body  that I use with lens removed as a
contact frame for step wedge tests. I use the 21 step 35 mm size wedge
from Stauffer, trim it to fit between the rails, tape it in place, and
shoot as many frames as I want, usually a whole roll, which I cut into
short strips for developer testa etc. I use the enlarger as light
source. I take an incident light reading right at the enlarger's lens
board with the lens removed. I use the exposure time calculated by the
exposure meter's dial by considering the focal length of the enlarger
lens to be the lensboard-to-easel distance and the diameter to be the
lens indicated focal length divided by the lensboard to easel distance.
You can play with these numbers to get a usable combination. Be sure
there's nothing in the negative carrier.

With this setup, you can make identical negatives from the step wedge.
You can remove the silver from one developed in pyro, develop another
strip in a non-staining developer, and superimpose any combination you
can think of  to your heart's content. You can use the bleach and
redevelop method to make a stained negative from one that was developed
in a non-staining developer. Be sure that  the bleach you use for this
process has brimide in it and do not use hypo until after you have
redeveloped the bleached negative in pyro.