A: December 15, 1911. According to the 2010 book Stan Kenton:This is an Orchestra! (on page 1; link is here) Kenton was conceived out of wedlock, and to cover this up his parents used the February 19 1912 date, a date Kenton believed to be true well into adulthood, but his birth certificate is correct and states December 15 1911. This explains why many sources give February 19 1912 and Kenton himself recorded a birthday concert on February 19.
