How to restore the AddressBook database from backup
First, the database file is ~/Library/Application Support/AddressBook/*.abcddb (with abcddb meaning Address Book CoreData database). The files in ~/Library/Application Support/AddressBook/Metadata have extensions like .abcdp (Address Book CoreData person) and .abcdg (Address Book CoreData group). The metadata files can serve as a backup if the .abcddb goes bad or missing. So if you want to restore those abcdp files, you need to:


Back up your Address Book data
Quit all applications
Move, rename, or delete the .abcddb file mentioned above
Put the abcdp files into the Metadata subdirectory listed above
Launch Address Book.app
Select and drag the contacts out to save them in one or more vCard files
Restore your Address Book backup created in step 1
Import the vCard(s) created in step 6


If you need any help or clarification on this technique, please leave a comment. I hope this works for you!