For that I'm not sure since I don't know which name Fakku usually use to tag the artist name, the doujin circle's or the author's. I prefer to use the circle's name though, in this case those would be Kabayakiya, MTSP, and Magonotei.
I also found a lot of duplicates in artist names caused by typos, caps, or different style of writing (e.g. Kouchaya & Koucha-ya, Outerworld, Outer World & Circle Outerworld). The easiest way to organize artist names is to check the
Sort by.. Artist page and just read down the list and check the artwork if you see any suspicious name, or check mugimugi if you're still unsure. Also, names starting with "Artist", "Circle", "Studio", or ending with "-tei" and "-ya" are possibly dupes.
For example, I just casually skimmed the first page and already got quite a few. Checked the doujins and confirmed they were made by the same artists.
I wanted to tell you guys about this since quite some time ago, but I realized putting on tags and naming unknown doujins are more important at the moment so I held back and eventually forgot about it.