Yes -- the original standard-definition frame to which was applied the Super Resolution upscale. (I wanted to compare your results from the starting point.)
[Thanks for the picture -- I just saw your update w/link when ready to post this!]
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BTW, thanks for posting that sequence of steps! While reviewing them, what came to mind was the wave-particle theory of light. So I quickly worked up a proof-of-concept in a paint program, which I thought you might find interesting.
The reason for "noise" on film (most noticeable when under-exposed) is that light can be said to behave as "particles". Light particles travel to and randomly hit the film, but in density proportional to it's "brightness". Less light means less hits or bits of exposed film -- dark and grainy (fewer exposed film grains interspersed between lots of unexposed film grains). As brightness increases, ever more hits increase the exposure of the film -- lighter and less grainy (more exposed film grains compared to fewer unexposed film grains). And the pattern of exposure is random from frame to frame, even if successive frames look the same. The result? Darker is "noisier" and lighter is "cleaner".
Why does film (like that with which we work) seem so uniformly grainy? From original negative, generational copies impresses their images, including the now built-in "graininess", on each next generation. The dark areas really don't get much more grainy (just more randomized). The light areas, however, accumulate ever more noise as part of it's picture. After enough generations, they saturate in graininess just like the dark areas.
Therefore, when "de-noising" a film to look as pristine as the original negative, the greatest strength should be applied to the lightest areas and the least strength to the darkest areas.
Also, approaching it from the opposite direction, when "re-graining" a film, the opposite is followed -- the least strength should be applied to the lightest areas and greatest strength should be applied to the darkest areas.
So ... for your re-graining, I wanted to see how it would look if the grain was added in proportion to it's brightness: most in dark; least in light. Thus ..
The 1st picture (150% magnification) is your step 3 final Super Resolution v7 -- short-labeled here as "regrain" & "regrain compare". In the paint program stack, it is the only one showing (the "open eye"). I would blink that solid layer on and off to compare before and after.
The 2nd picture has all the other "eyes" open. It used your step 2 Super Resolution v7 with grain/noise removal, here short-labeled as "no grain", and your "regrain" to isolate your added grain, to be put back a new way:
* Group inverts no grain
* Group - add grain dodges Group into no grain = isolates (added) grain from step 3
* Group - add grain burns isolated grain back into no grain
dodge and burn are paint program functions that work based on image brightness -- perfect for pulling out grain/noise and putting it back in, both in light proportion. Accuracy is not precise, but for quick test in a paint program, you can get the idea.
SW GOUT SuperResolution natural regrain [click for full picture]