Unfortunately our manual is a bit outdated in certain parts. Lack of man hours, and nobody steps up
. That being said, I can't even remeber such a thing as gpg files to check integrity. So they must be gone for a lonmg time (if they ever existed).
And to be completely honest with you: I downloaded and installed thousands and thousands of images and never verified the image unless it was faulty. And from those cases, I cannot remember one being faulty due to a failed download or to a image that had been tampered with. I guess I got lucky as I hardly ever download Mint Linux