I would only add that "holdback" is in the eye of the beholder, as well as "collector" quality. It is very subjective and depends on the quality of the breeders and the comparison between it's clutch mates. Dragons will be held back due to color, pattern, size, morph, or sex and be given time to develop before sold (at which time it looses it's "holdback" status, heh).
I have noted in a lot of cases that what most would call a holdback would be just a normal in our clutches.
Careful research and shopping can pay off, but most of the time you get what you pay for.
Jeff