Just had to debug a little issue with a domain that were not considered authorative from our DNS server. The SOA records were there as they should be, and it referred the correct name server in the SOA record. A bit of searching at Google later turned up the cause of the issue; the name server did not have an NS entry for the domain. To be considered authorative, a domain server has to provide an NS entry for the domain too. As I do DNS stuff only a couple of minutes each year, details like that happily slides away to the darkest corners of my mind.
So to sum it up: Get your SOA and your NS records straight, and you can be authorative all day long! Authorative like it’s 1999!