Why is the Edition unknown?
We only started recording the edition of books around the start of February 2007, so if the book was added before this time then unfortunately we won't be able to display the edition.
Books that have not been added using their ISBN will also not have the edition displayed.
If you want to add the edition for one your own books, go to My Books and click "Edit Details" beside the book. You can then enter the ISBN and get the edition.