Bullet journalling was introduced 9 years ago. I know because I remember the very first website and how it totally transformed how I did things at work. The website was built to tell you how to use the system. 9 years later the idea has expanded into a course, books, communities and newsletters.
Very cool, except the most basic of things, a reference guide to the system is nowhere to be found. I think this is a colossal loss and missed opportunity. BuJo should be about the system first and foremost. Let those that can benefit from the simplicity of the system run with it.