Malcom,
When you find an aircraft that is not in the Database go to the home page and enter the registration in the "Search Tail Number" box It will then give you the option to enter new data. Click "Yes" and fill in as much information on the next two pages as accurately as you can. If you do not know leave it blank of if it is required enter 0000.
You may want to delete the entries that you found with no data and start over with those.
If you have no information just put UNKNOWN in the registration box on the upload page. Then put as much description as you can in the description box.
Easy enough!