It's a matter of luck, really. I have eight characters, and only my main character managed to kill all dragons. And that was taking into account the APs I got for him from the $10 in credits I purchased (I do that every month as a way of supporting DT). My alts didn't get APs from those credits and none of them got the 10 dragons. Granted, each one had a small stash of credits and got some extra XP, but with no luck.