I thought they had pushed it back further than that?? I only keep in touch with dendrochronology somewhat peripherally to my interest in isotope age dating. Once upon a time I used to do some sample prep for C-14 dating, and in a totally unrelated research connection (unrelated to C-14 dating, that is) had a chance to work for a short time with Willard Libby (who developed C-14 dating). A genius of a man even in his later years (I think he was over eighty when I worked with him).