So the Book of Daniel was in the Dead Sea Scrolls?
Most of it. Oddly, while the apocryphal portions are present, the DDS omit chapter 12, even though one midrash scroll refers to it. So the evidence suggests that chapter 12 may have been the last to become cannonical, not the apocryphal portions.
-—>>>NOTE
It has come to my attention since writing this that The Prayer of Azariah and Song of the Three Holy Children is included in context in a DSS scroll (located at Daniel 3:24-90), and Susanna and the Elders exists as a preface (the Vulgate makes it chapter 13). But the story of Bel and the Bronze Dragon (placed as chapter 14), while present in the DSS, confirming its antiquity, is not found in the context of the rest of Daniel.