1/ Koryu are schools created and transmitted before 1868 when started the Meiji era. They are old schools of the old age. At that time bujutsu were samurai knowledge. So it is samurai tradition. To my understanding.
Nice post, Philippe. I personally see no overriding difference between "koryu", "traditional styles", "family traditional styles", and so on. The longer a 'school' has been in existence, technically, the more room there is for deviation from the original teachings. I know of a number of very ancient "traditions" which have deviated all over the place. The idea that someone is 'preserving' something unchanged from an earlier time and culture makes me wonder if we're living on the same planet.
As any pragmatist will point out, no robotic teacher ever produced exact robotic copies of itself. Even modern martial-arts barely get past one generation without a number of permutations, loss of knowledge, etc., slipping in. Look how many of the "direct students of Yang Cheng Fu" teach very different arts; look how many "uchi-deshi of Ueshiba Morihei" teach very different arts. Someone wants to tell me that I'm a "jerk" for thinking that some koryu isn't subject to the realities of life? I think it just got proven.