The Bible is revelation upon revelation. Each prophet of the Bible received revelation after his predecessor. Since Deuteronomy was written by Moses, then by your logic, the rest of the Bible is illicit. And the book of Revelation was not the last book written, it was only placed as the closing book.
In short, those statements are spoken in regards to those who would change the words of those specific writings; the Bible, as we have it, was not known until well after the last of any of the books of the Bible were written.