All of the other stuff wouldn't be documented because it wouldn't have been important at the time. Back then, they wouldn't have given certificates to students like we do now for training. Most documentation if it did ever exist was probably destroyed in the Battle of Okinawa where the US bombed the crap out of the country destroying almost everything. What we have left are just a few personal journals that survived that are related to other items. Also, I didn't state that Koshankin taught a style called "kusanku", it is known that the kata was created after studying with a chinese master and taking certain lessons from him.
In other words, no documentation then.