Duplicate works uploaded by different artists

There seems to be an issue with gochou_(atemonai_heya), the original artist I presume, having his works copied and upscaled by ayuya_naka_no_hito as shown in the parent and child of post #1637494 and post #1570680. Is it possible to identify whether if the former artist is using two accounts since the description commentary I've seen don't indicate between the two.

I want to clarify this since post #1666250 by ayuya_naka_no_hito has also appeared in gochou_(atemonai_heya)'s pixiv and it will make it confusing on which work is whose.

"Ayuya: Naka no Hito" actually means "The staff of Circle Ayu-ya".
あゆ屋 (Ayu-ya) is a doujin tabletop game circle led by Kitazaki Ayumu. (He is not an artist.)
Gochou was offered an art commission from the circle.

So should such commissioned uploads be tagged by the respective artists, the pixiv source or by both?

The name of the artist who actually drew the image.

I went through ayuya_naka_no_hito's posts and re-tagged them with the actual artist.

However there are still 6 posts, all of which he credits the artist as "さの". Anyone have any idea who this is?

I'd hate to create an artist tag that's just "sano" with no disambiguation. But right now there's basically zero information about this guy. No homepage, no pixiv, no twitter.

I believe さの is sanoharu. That's their pixiv username, ayuya_naka_no_hito is following them and the art style matches.