Actualy it now states all that about Yoda training the kids in the databank entries at the official site. Seems when the lickle kiddywinks first become padawan they are trained by the froggy one. Then as El Chux said, they are partnered with a jedi master at around 13. So yoda at some poibt is every Jedi's master. And they just continue to refer to him as he is the big cheese in the Jedi order. Perhaps it would have been clearer if Yoda had been a grand master but that sounds un jedi like to me. more like a dark side self agrandiosing title.