LOL, Kiwi beat me to it, but yeah.
I wouldn't call the Retro sites "another scanning project," implying that they share a commonality with sites like Retromags or Oldgamemags which feature ONLY stuff we've scanned ourselves. It's true that a small percentage of their files are their own scans (mostly Akane's files), but the vast majority of their stuff has been copied from elsewhere and as Kiwi pointed out, until the last year or so, they would always ruin the quality of everything they "mirrored" by shrinking the filesizes down. So you're usually better off downloading all but their most recent files from somewhere else. The biggest problem asises when other sites mirror the corrupted Retro files, which results in one big flustercuck of bad-quality files being spread around the Internet, which is the main reason I was always opposed to them changing the quality of the files they "mirrored." (Luckily, as I said, they no longer have a policy of shrinking files and allow for full-size scans to be uploaded as is. Unfortunately, all of the files they host that were uploaded before their policy was changed remain compromised.)
Those PC Engine mags have been there for ages. I honestly have no idea if they originated from the Retro sites or if they copied them from somewhere else, since they don't credit scanners. At any rate, don't feel as if you can't upload all of their files to archive if you want to. They certainly have no problems mirroring Retromags' files days/hours after we upload them, so they shouldn't have any problems with their own stuff being mirrored in as many places as possible. Again, though, I'm not sure if anyone at their site would deserve credit for scanning those particular files. Maybe one of their uploaders could comment on who the scanner was?