The Clutch of Dragons, pg 121 'The War Room' (fiction):
In this story, featuring Lofwyr, Lung, Arleesh, Aden, and a whole room full of younger dragons the text mentions that three of the younger dragons were within a few years of becoming Greats.
Same book, pg 137 'true drake' (character quality):
The book describes these true drakes as drakes who are closer to the original blueprint of drakes that Ghostwalker put together way back when. The book does not (that I could see) show any way for a normal drake to become a true drake, but rather gives the information for those GMs who might be touched in the head enough to allow one as a PC or to give them the ammunition to take on PC normal drakes).