Thanks! I honestly don't know if multiples were done, but I checked the tones in the watercolor against the images of the cover I could find online and it's a spot-on match, I'd be super impressed if there was more than one of these things! It even has all the rough strokes on the back of the board where the artist was testing the brushes or laying out the palette... which is just a total trip to see. The acetate overlays have the line work on one layer, and then the date and prices on another, with tracing paper over that to make final edits. Not having much exposure to pre-digital commercial printing, this was a side of the comics I'd never got to enjoy before.
That swamp thing separation sounds awesome, love to see a picture sometime.