We have to remember not all dragons reproduce all the time. Some of them have not even reached adulthood yet....you're not going to see a hatchling running around making babies....that being said lets limit mating to twice in a given dragons life cycle and that should keep the population in check....also I noticed that my own math was in error there would actually be a fair few Dragons in the Capitol given that there are 12 families and one set of parents has 3-4 children....twice, and then they have 3-4 children twice, so there are actually a rather high number of True Dragons running around even with personal conflicts leading to "early" deaths.
Also by the time I actually get a chance to sit down and edit the Wiki there is going to be a lot more stuff to put on it.