I have tried to read up on the dragons of the sixth world as much as possible, but I there are some mysteries that make things unclear.
1. Are all the Great Dragons in the world known by the metahumans of the Sixth World and accounted for, or are some Great Dragons only known in the deepest Shadows?
2. When Ghostwalker came out of the astral were the other dragons saying "About time?" or were they surprised?
3. When the dragons gather, as they have when the title of Loremaster was contested, do they do a headcount and find some lesser and greater dragons unaccounted for since the Fourth Age?
4. I know it's been kept vague, but how does a lesser dragon become "Great?"
RE 1:Who knows? The dragons ain't telling

It was rumored in a fluff piece that the Immortal Elves spent a large part of the down time hunting down and killing the sleeping dragons (hence why the IE and dragons do not get along very well for the most part)
RE2: From what I remember, it wasn't unexpected that Ghost Walker would return, the question as "when".... and while I doubt they expected him to burst forth from the site of his brother's death, his return was expected.
RE3: Going back to that fluff piece about IE killing dragons in the down time, I guess there are quite a few unaccounted for dragons.... But who they were, where they are, or who they expect to show up next, just isn't public knowledge

So who really know outside of the dragons themselves? The dragons are not talking, that is for sure.
RE4:it's apparently the last stage in their development... So when a little baby dragon is all done growing both mentally and physically they go *poof* and are now a great dragon

(see my above post)