Where did it say that they have to be magically talented? I understood every child born in those hours would be a starborn, and there are many, many people born in any given hours. Most starborns would never heard of outsiders, and those who do and have no magical talent would probably die fighting with normal weapons. But a few of them will be really dangerous for the outsiders.
Also, 643 may be Merlin?
On a side note, if it is every 666 years exactly, it has been Halloween for a couple of times. Perhaps it is what originated Halloween.