Quite. I think it's easy to overlook just how much of a challenge something like this is — with plain linework, clean-up is relatively easy, because it's (pun intended) black and white. You either want this thing or that thing to appear on the page, or you don't. With all these lovely grey washes, something as simple as tweaking the levels or the contrast to bring up the whiteness of the paper risks buggering up the grey tones in the art completely…
Yep, that's the difficulty with this type of artwork. With something like, say, The Dracula File, I could be aggressive with levels etc. to get the whites/blacks to pop (though even there it still needed a degree of manual "repainting" to remove scruff and tidy up blacks that had badly faded) and you can get more aggressive with sharpening/resampling tools to get the linework looking nice and crisp, but with this it meant blowing the detail and subtlety in the greywash.
Most pages therefore needed a gentle level adjustment to bring out as much of the white/blacks as possible, then there was nothing for it - if we wanted to preserve as much of the subtlety in the greywash as we could - but to go in at full magnification and "paint out" the areas of the page that were originally supposed to be white/black, preserving as much of the greywash as possible. I spent rather a long time staring at screen-size patterns of half-tone dots!
What we do with these books will never quite match the quality of being able to work from fresh scans of the original artwork/film, but since that is long scattered to the winds we use what we have and work as hard as possible to present it in the best possible light. I've always been very impressed with the work Kathryn Symes does for Rebellion, and the approach and dedication she brings to her restoration jobs - often working from page scans too, where original film or art is damaged/missing - is the kind of target I like to aim for. Hopefully we hit it more often than not!