How do I add finds for unlisted boxes?premium member, you can't. Being able to list all finds, regardless of whether the letterboxes you've found are listed on Atlas Quest or not, is a premium member perk.
If you are a premium member, or happen to get in on a "free listing day," use the Record Find option from the Letterboxes menubar option. Type in the name of the box you want to add and set the type of letterbox you've found. If you already know the letterbox is not listed on Atlas Quest, do not worry about the author. Finds of unlisted boxes do not track the author of a box, so it won't do any good.
Atlas Quest will first return a list of letterboxes that match your search that are listed on Atlas Quest, but skip below that section for a list of matching letterboxes that people have found that are not listed on Atlas Quest.
If you are the first person to record finding an unlisted letterbox, you'll have to use the "create a new entry yourself" option next to the Unlisted Letterboxes section.
Fill in the rest of the blanks and save your find.