User blog comment:IamJakuhoRaikoben/Chapter 415: And It Shall Become Your Will To Live, Review./@comment-4489126-20150110171805/@comment-7418318-20150110172135

Good question.

Considering their words about the Age of Dragons being over, I'd say that the Dragon Parents didn't know about any survivors which most likely means that it is a very small number only.