Thanks for the MCS link. I reached out to CGC to get some clarity as I have a set of these books in the grading pipeline. Here's the response from their grading department,
"Yes, any copy of SUPERMAN/GEN13 that has a cover by J. Scott Campbell and is *not* labeled as a Variant Cover is incorrect, and we will fix any that are returned to us.
The confusion initially arose because the UPC codes for the both the regular covers and variant covers are the same. It's only on the letter's page that the J. Scott Campbell covers are specifically listed as variant covers."
MCS states as such under the notes at the end of the regular cover of #2 & #3, but not #1.
https://www.mycomicshop.com/search?TID=261051