Constant Contact identifies contacts by their email address. Likewise, contacts are linked to the database from Constant Contact by email address. If two people in the database share the same email address, their Constant Contact listing will only show one name, but they will be both be listed as linked to the Constant Contact record.
If the email address of a person entered in Constant Contact does not match the email address assigned to the person in your database, they will not show as linked on this screen. To fix this, either change the email address in Constant Contact or add the email address to the person in your database (in your database, a person may have more than one email address).
You can update records in Constant Contact (by going to your Constant Contact account on the Constant Contact website) to reflect two names assigned to the same email address (e.g. Entering “John & Maria” for the first name).