Talk:Game Updates/@comment-27921111-20170323194039/@comment-5760976-20170323194528

As quoted from Kaleni himself "After the Egg of Mystery is purchased, it will transform into a random dragon egg. This could be a dragon you don't have or one you already possess."

That means there is a chance you can get a dragon you already have, even if you still need some dragons. At least, it seems to be that way.