The first thing to look for when it comes to such people is the way they are treated by other established members of the group. In Koryu, how do they fit in with other Koryu people, for instance. And, once you get into a certain area, you will find who is respected in the main pretty quickly. See how the "self proclaimed" person compares - do they say similar things, or wildly different? What do other people in the field think of them? Are they respected in return? And you will often find that, even if there isn't official journals, there will still be something similar, a peer group based around discussion. Such as this one: http://www.facebook.com/groups/195458010500646/
Perhaps that is the way it is in koryu, but I do not know if you can take that and apply it to a different art or culture, like the korean martial arts. I don't believe there is any sort of official journal or a peer group on korean martial arts history. If there was one, I'd like to join.