...

(For clarity, we will call this "Contacts.app".)

What is a "unified contact" 

Contacts.app will attempt to identify people that appear in multiple stores, and display them as a single contact.

https://support.apple.com/guide/iphone/hide-duplicate-contacts-iph2ab28320d/13.0/ios/13.0

https://support.apple.com/guide/iphone/hide-duplicate-contacts-iph2ab28320d/12.0/ios/12.0

Where is the original data?

...