Original and Unknown series of Hentai

How come both the Original and Unknown series exist? Why not consolidate the two into the already 378 doujin giant that is the None series?

here's some links to what I'm talking about:
Original Series (for some reason doesn't work for me but you can find examples on the front page)
Unknown Series
None Series

Now that I'm double checking it, seems that all those "original series" are indeed tagged "none" but the links on the front page are misleading.

Yeah I'm still figuring out how we are going to do this. Unknown series just means that it is based on something, we just aren't sure what.

Original/None means that it is an original story, meaning the author didn't base it on an existing anime/manga/game.