Actually this commonplace is only true if Ezra-Nehemiah is counted as one book, as it was in ancient Jewish tradition because they were written on a single scroll. To be sure, the Books of Nehemiah and 1 Chronicles have not been found either, but they are generally assumed to have been present on the basis of the few crumbs of the scrolls of Ezra and 2 Chronicles. But see Sidnie White Crawford, “Has Every Book of the Bible Been Found Among the Dead Sea Scrolls?” BR 12:05.