When this flag book was posted on the Bookbinding Team blog, Olive Art commented with a question of how I attached the button and thread. I gave a short description; I attached the button and string by punching a hole through the cover board and the valley of my first accordion fold. I used one length of string, with the ends knotted underneath the button.
But after writing that, I thought it might be nice to offer a visual description.
Click on the diagram above for a larger view. If you start with the red arrow, you should be able to follow the path my thread took.