But doesn't this refer to the interior work on the books after a certain point? I don't remember reading anything about the cover work being done this way.
I don't think we can assume the covers were done the same way the interiors were.
I used to think that until I reread that BackIssue #21. Janson, in that DD article, describes what techniques he used to get the desired look/mood for the book. Using two pieces of comic board and ink wash sounds like something he would do. Not saying this isn't a Miller piece, I'm just saying.