In Japan there are ofter parallel promotional systems.
In the Japan Aikido Association University students that have trained from the beginning of their studies promote to Shodan at the end of their second year so they have the BB in their last. A few get promoted to Nidan at the end of their third. In some Universities training is required every day. At Honbu on the other hand Shodan usually takes twice as long and even longer if your attendence is only once or twice a week. It took me three years at Honbu even though I already had one year in the University clubs.
I did mention it in on another forum but will do so again. Kenji Tomiki did form his own organization and establish his grading criteria but he never took rank beyond what his teacher Ueshiba gave him. Kano never took rank but once he died he was awarded 12 Dan as sort of an upper limit.