As per my comment on that thread - the information presented is from a single point of view and not necessarily the whole truth.
I understand that Inaba sensei had 17 months of training with Kunii sensei (thus 1.5 years which is quoted elsewhere - certainly more than the "less than a year" dismissive comment). The certificate he received was posthumous (of Kunii sensei). As I understand it, some (personal) communications (between Kunii sensei and Inaba sensei and others) shed a slightly different light to the statements in the blog entry - more than that I cannot say without breaking confidences.
Life is not always simple - especially when you include people and their egos
It's not just that 17 years is "more than 'less than a year'"...it is quite sufficient time for a master swordsman who is reasonably good at teaching to turn the goods
over to a bright student. Particularly if that was 17 months of daily training sessions, and the teacher and student had a very good rapport, which are two things i have read allusions of.
The rule rather than the exception in the life of the koryu in modern times is: the headmaster dies, and some number of senior students fail to find adequate motivation to follow the new headmaster. Since every ryu has its own unique criteria and process for licensing, you wind up with some talented individuals without menkyo kaiden going outside of the umbrella of the ryu. And if they happen to attract lots of students and build organizations, the reaction of the folks back at headquarters is going to range from dismissal to petulant derision. Which can then be magnified by foreign students who grew up in cultures where people speak their minds more plainly than they do in Japan.