Here is the official response from CGC regarding how we graded the books.
We apologize for the short response yesterday and wanted to follow up with an explanation of our thought process behind the grade assignments. We treated them as we would any other variant cover that's attached with an extra set of staples after the book was printed, and at times these books included the original cover as well.
There is a precedent for acetate covers being attached to a printed book, and then graded by CGC. An example is Stray Dogs #1 from last year. An acetate variant cover was attached with an extra set of staples, to which CGC assigned a Universal grade and a notation of “acetate cover” on the label. The extra set of staples were part of the manufacturing process of attaching the acetate cover, and not considered a defect.