Deciding when to pre-populate a Core Data store is a real headache when you need to sync that data store across many devices. However you can learn from my experience and save you the headache that I had to went through.
Introducing the Core Data Controller
Here is a document class replacement for managing your library-style app based on Core Data. All the goodness of NSDocument / UIDocument with just the right functionalities when you don’t need to expose document-management functionality to your users.