I just found this in Old Testament Abstracts. I'm sure the WTS "scholars" will snatch it up in a second. Since the article is in German, I can't examine what it really says and what its take is on the birthdays in Job.
ANDREAS LEHNARDT, 2003. "Zum Geburtstag in den Judischen Schriften aus hellenistisch-romischer Zeit, im Neuen Testament und in her rabbinischen Literatur," Judische Schriften, 402-28.
"L. examines the idea of the 'birthday' in Jewish literature of the Hellenistic and Roman times (mainly 2 Maccabees and the Psalms of Solomon), in the NT, and in Rabbinic texts. He concludes that compared with the literature of the pagan Hellenistic and Roman world, the concept of 'birthday' plays a relatively small role in ancient Jewish writings: Although life is not devalued, celebrations of the birthday of pagan or Jewish rulers are viewed negatively. Since a person's 'birthday' is seen as the day on which a human being becomes able to sin, it is rather the day of one's circumcision that is to be celebrated."