If you have any questions, please ask me and I will research them as best I can and post the answers here

1. Why isn't "kodona" on your site?

Because it's not a fashion in Japan.
please see full explaination here

2. Is there such a thing as "horror lolita"?

This one was hard~
There really isn't a term "horror lolita", or a "horror type" lolita.
However, on an instinct I decided to search for "grotesque lolita" (gurololi) and came up with a few hits.
It appears this is one of the less used terms, and is reserved for the girls who walk around in bandages, chains, etc with fake blood and scars.
They tend to lean more towards the "gothic lolita" side, and can sometimes be considered "painful lolita" or "cosplay"
It's not important enough to be added to the guide, since it doesn't appear to be widely used, and could thus be a term used by a certain group of friends or an online community.
But yes, it does indeed exist ^^ I hope that helps~