A work may have been created by two or more authors. In Safe Creative it is possible to record new authors in a work's registration so they will appear both in the information page and registration declaration to be sent.
Whether the work is in registration or pre-registration mode, simply go to "My registrations" view of your works and select "Inscriptions". A new screen will open; select "invite coauthors". A window will pop up and there you can add the email addresses to which the coauthors will receive the request to join as coauthor. They can accept it, or not, by logging into their own account, or create a new one if not having one already.