"Everything applying to Koryu systems should and can be validated"
Not necessarily. Some things can be verified through generally accepted history. But as for who is legitimately teaching Koryu, for the most part it's just a matter of whou you choose to believe. The politics has made it that way.
Take a look here at the Kondo Sensei thread in the Daito Ryu forum. Kondo Sensei is seen by some, including Aikido-Journal (a respected publication here in the U.S.) as being the inheritor of Daito Ryu. Now they try to paint other Daito Ryu teachers as illegitimate or atleast not teaching Daito Ryu. Yet, it is quite common knowledge in Japan that there are problems with Kondo Sensei's claim. So who do you believe?
I was just looking today at another well known and respected koryu web site. They have information about 2 koryu systems, 1 Kenjutsu the other Iaijutsu. I know that both articles contain fabricated information. The one person who they are holding out as "Soke" has changed his own training history on his own web site several times over the last few years. Also, his "sokeship" is widely disputed in Japan. But anyone looking for information on these styles may very well end up not training with a legit teacher based on the politics of this web site publisher.
The same publisher had an article that discredited a very well known teacher of Ninjutsu. Then they started selling books on the web site of one of this teachers students. Suddenly, that article is gone.
The Budo has become totally corrupt and polluted. Rank, titles and now even history and lineage mean absolutely nothing outside of your own dojo.