Time is not what is important, it is the journey that counts. Yet 9 years is a long time to Shodan.
I believe Master Mitchum received his Shodan from Shimabuko Tatsuo during his 1st tour (USMC) in Okinawa which was about 15 months long.
So why 9 years now to do what was done by others in a much shorter time?
My sensei trained under both Masters Mitchum and Harrill. He said that they told him they were given their black belts at the conclusion of their Okinawan tours (they were both Marines, as you know) with the instruction by Master Shimabuku to go back to the states and train, and in 10 or 15 years, they'd be worthy of the rank he had given them. At that time, some feel that Master Shimabuku did not know that they would open dojos and begin training, or that he would ever see them again.
My dojo is a volunteer effort, run as a sideline to my sensei's main business (he is a pilot). It loses money. No one who works at the dojo is paid, it is all strictly voluntary. It is a very small dojo, and we are told that if we want rank, there are place to get it. This is not one of them. They teach karate there, and belts come when they come.
There is no 'rule' that the time to black belt takes X number of years at my dojo - it's just that Sensei Holloway has promoted very few people to that rank, and that's about the average time it has taken. Some quicker, some slower. One man, I am told, made his first dan in four years - one took twenty years.
I do not know for a fact, but I suspect that the length of time it takes to get promoted at my dojo is my sensei's way of keeping belt-seekers away. He only wants people who are there to learn karate, not those who seek validation with a belt or a certificate. But that is just my opinion, he's never said anything like that.
We are told that when Master Shimabuku first started training Marines, there were only two belts, white and black. I would be content to remain a white belt, but we do have a system of promotion, and one of my senseis told me he was sick of looking at my white belt after six months, gave me my test, and told me I passed. Tomorrow night, if Sensei Holloway agrees with his recommendation, I guess I will be awarded my orange belt. I'm grateful, but it is not the belt that I covet, it is the training that I have received and continue to receive. As to belts, I am content with whatever my senseis believe I have earned.