I could be mistaken about this-- if so, I am sure I will be corrected. When reading about the 9 traditions of the Bujinkan (3 ninjutsu traditions), I have often noticed that usually Togakure Ryu is listed as Togakure Ryu "Ninjutsu", and the other two are listed as Gyokushin Ryu "Ninpo" and Kumogakure Ryu "Ninpo". Now I realize that this isn't 100%, but I have noticed it enough to make me wonder. Why would one tradition be called "ninjutsu" and another tradition "ninpo"? Ofcourse since the latter two are kept secret we could only hazard a guess. (And, are those 2 really secret? Has there been any exploration of them?)
Blimey Marshall, a well thought out question!!! I found this in the first instance which gives a difference. http://www.ninpo.org/ninpo/ninpo.html They are kept closer to Japan, not so much a secret but not something you will learn from a 2 week visit, i believe if you live out there or are further up the scale or closer to the source this is taught.
Since the words Ninjutsu, Ninpo and Ninja AFAIK are relatively modern terms then its highly unlikely these terms i.e Kumogakure Ryu Ninpo, Togakure Ryu Ninjutsu etc would have ben used in the past. Its more likely they would just have been Togakure Ryu, or maybe just the "Tradition of Togakure" or something like that. I think today we make too big a deal out of all these terms, and end up tying ourselves in knots with them. Its a bit like how we might use the terms Unarmed Combat, CQB, Self Defence to explain the same thing. Gary Arthur