Contacts not appearing on mailing labels
This was due to an import bug. During the import some contacts were set as deceased (value 1). The remaining contacts were then set to null by the import tool. But all the elements like Do Not Email if Deceased require a value of 0 for the deceased field. So they wouldn't show on the mailing labels as the system thought they were deceased. A simple export of all individuals (contact ID and deceased value), remove those who are deceased and re-import with a value of 0 on the deceased field solved the issue. –