Anyway, back to the discussion, but not to add to the hefty tome that the previous thread became, here is what I deduced from it (and from other non-nerdy-internet sources).
The named ryu taught in the X-Kans are koryu, because they are 'ko' and they are 'ryu'. The X-kans are not koryu as a whole because they are umbrella headings from umbrellas that were not put up until the 20th century. The argument that rages on is about whether what is taught today is the same as it was hundreds of years ago with only minor changes and evolutions (I gather that it was more customary to rename a ryu if a master altered it considerably).
So no, the Bujinkan is not an 800 year old martial art, but some of its components are. Some of the X-kans emphasise the separation of the ryu more than others, and the big Booj itself seems to be the last of all to have done so, with Hatsumi sensei saying once that he had no intention of doing so (until it looked marketable, or at least that is the opinion of some!)
The koryu snobs have no more proof than any X-kan headmaster that what they do is exactly the same as their Japanese ancestors did and it would be somewhat sad in any case for a martial art to have done nothing more than stagnate for the past five hundred years.
Most of what is accepted as koryu nowadays is based on the state of ryu that survived until the Tokugawa era, when idealistic non-combatants of the Tsunetomo Yamamoto variety decided to stylise everything and almost eradicate the battlefield effectiveness of Japanese martial arts. Samurai hardly ever charged fearlessly to their deaths, but ran away when the going got tough. Bushido didn't exist for the original bushi, and nobody had the luxury of studying for 40 or 50 years under one master or learning many (if any) kata as such. The move to 'do' forms has largely exacerbated this lack of martial continuity, so that in the present day, none of our martial arts resemble the arts of the same name as they were under the first couple of soke. Look at how much of what is today called iaido or kendo would be effective in armour, and how much is geared towards the street encounters and duels of more peaceful times in Japan's history.
And surely yarijutsu covers all the spears, whereas sojutsu is for soyari/suyari. There were many names for unarmed combat and other arts, why not the spear?
Adam C R Hurley -
I know nothing - Manuel, Fawlty Towers.