How Open Contacts update an existing contact when importing
A contact is uniquely identified by the full name, surname, given name and middle name. When importing a contact with the same name existing in the database, OC will prompt the user for action. If the user choose to update existing record, OC will try to merge:
1. If an imported field (combination of section name and field name) does not exist, the field will be added.
2. If an imported field does exist, the field will be updated.
For example, Andy Smith in the database has
Personal/Phone = 4324324324
And the imported Andy Smith has
After importing, the existing phone field will be updated, and 2 more are added, so the personal section will have 3 phone fields.