So, when I remove a rear drum then crack open the bleeder. There will be no fluid expelled ,and absolutely zero movement of brake shoes via wheel cylinder contraction as stored pressure is released? That seems like what you're saying...
Pretty much, you mention "absolutely zero movement", well their might be a couple thousands of movement.
The "sticky" part about understanding hydraulics is that we're all conditioned to think about pressure as something like a tire, where if you increase the pressure the tire expands.
But air compresses, and fluids don't.
A solid column of fluid, (no air,) wont matter if it has 10lbs or a 1,000lbs of "pressure" on it, when you release the pressure the fluid wont expand.
You can open the bleeder valve and release that 10lbs, but the fluid wont come squirting out, because their is no compressible air or gas above it that will expand and push the fluid out,, that's why 100% bleed jobs are so important.
If the brake line has ZERO air in it opening the bleeder should only let-out maybe a drop or two of fluid,, and that do to gravity.
Another thing is that when the pads and shoes are in full contact with the discs and drums their is NO more movement of fluid, their is only the transfer of pressure thru the fluid.
Because the pads are already starting out in contact with the discs, the only "movement" of fluid by the MC is just the amount necessary to expand the shoes into full contact with the drums.
Those videos that show the pads pushing-out to touch the discs when you push the brake pedal are false, actual pad movement is very tiny, on the order of thousands.