Where to find the thrid site collection administrator?

When either the server or site collection administrator (depends on you have self-service turn on or not) creates a new site collection, the administrator has two field to enter at least the primary site collection administrator. This information is saved in the OwnerID and SecondaryContactID.

After the site collection is created, the site collection administrator is able to remove, change or add more than two site collection administrators to the list. If you remove a name from the list, MOSS will remove it from one of the column. When you add the same name back, or add the 2nd administrator to the list, you will not see the column updated by the system.

On the other hand, since there are just two columns, where the setting is saved if you add another administrator?

This is actually what happened when you make changes to the site collection administrator list:

1. When you add up to two names to the fields during site collection creation, both names are saved in the Sites table.
2. When you remove anyone from the list after the site collection is created, MOSS will remove it from the Sites table.
3. If you add a new name, no matter this is the 2nd , 3rd or more, MOSS will not update the Sites table.
4. All the changes made to the site collection administrator list go to UserInfo table. There is a column called SiteAdmin and this is the place you can do your search.