From what I know and have heard from a friend that actually got one of those blood tiles, there is a camp which can spawn outside of wrong (and apparently some other places), where a set of two blood tiles spawn which can be picked up. Also according to that friend, the camp spawns for only about 20 minutes, every month or so, which is why the blood tiles keep on being pretty rare.

But as I wrote, it´s from a friend, not sure if it still spawns or not (apparently it does, but I have no proof of it and he picked up his a while ago) and that´s only for the small blood tiles which come it two-part sets.

The server birth rare is the blood tile which is for the wall, which looks like it´s really dripping down. That really was duped countless times..

True duped items didn´t get deleted, only the "changeling duped" shrouds had their appearance change.
(true dupe = exact copy of an item. there is no way of telling which was/is the original and which not)