Thank you for reaching out to the Community. Many cases when a contact shows as opted out and he/she did not unsubscribe, it's usually because due to the email has been forwarded. The recipient of the forwarded email may have Unsubscribed or Reported the email as Spam. Doing this will unsubscribed the original contact who forwarded the email.
I understand how important your contacts are and would be happy to look into this further for you. Please email us any new contacts who this has happened to at social_support(at)constantcontact(dot)com with your username, the contact emails, and a reference to this post.