To the Gabriel stone, it is my belief that "so what" if it's dated to 4 b.c. which it so happens to be. In that same year Jesus was proclaimed to his family in Nazareth by the angel Gabriel. To me it goes hand in hand, the story. What if in Bethlehem which is fairly close to the Qumran community, that a scribe got word of the proclamation and wrote what was said to Mary down... That's just my opinion.