HonoraryBookSniffer

So i have been searching my bookshelves for first editions, and i know how you do it and everything. If it doesnt have First edition written you look at the number line. Well i was looking and i found a book in which the number line only has one number? It is litterally just a 1. i know it could just be a typo, but im just a touch confused. I searched the internet and found nothing. Can anyone shead any light?