While the great Saulo Ribero has a famous book that categorizes technique by belt rank, there's no such official testing or division of material in Brazilian Jiu-Jitsu.
There is no list of particular techniques that make a blue belt or a purple belt and so on. We're all doing the same material we just do the various moves like blue belts and purple belts. We are looking for a certain level of successful survival however, and that is evaluated dynamically.
You can only be evaluated for your rank by a community of practitioners of your art, the same way it requires an internship under a master of welding, pipefitting, or diving to learn to practice those trades well.
People vary in degrees of athleticism and time they can devote. They also vary in patience. Impatient people have a tendency to not give themselves enough time to get good at Brazilian Jiu-Jitsu. Doing anything well takes ridiculous devotion of energy and time. Playing a musical instrument or playing chess at a master class level requires hours of painstaking study and performance. No one is born with great skills. They maybe gifted with long legs, or an aptitude for retaining physical memory, but in the end the skills still have to be developed, and this is especially true of this game of Brazilian Jiu-Jitsu.
The business people involved in teaching BJJ teachers how to make money (and believe me we need all the help we can get) make a big deal out of not letting new folks train live for six weeks to a couple of months. The reasoning is that new folks are too often fair sampling of Judo or even weapons!) in those days we thought of all the belts below black belt as essentially the same thing–the "kyu" grades.
Today things are a bit different. Expectations from the millennials (so I am warned! Sorry to pick on your group!) are famously: looking for daily promotion! I'm sorry BJJ can't supply that. But we can supply lots of fun, a good work out, and a strong self-defense
background. You don't need any books and you don't need any time spent on the internet.
You don't even need to read these posts. What you do need is time on the mat with a qualified instructor. I'll see you there!
Geoff Balme is a second degree black belt and the lead BJJ instructor at Open Guard BJJ, Kickboxing, and Self Defense Classes in Apex, NC.