Well, I have learned to examine carefully anything the Watchtower really gets excited about and presents as beyond dispute.
Hippolytus was a disciple of Iranaeus, and he was a disciple of Polycarp, who was a disciple of the Apostel John. Around 204, Hippolytus wrote that “the first advent of our Lord in the flesh, when he was born in Bethlehem, was eight days before the Kalends of January, the fourth day [i.e., Wednesday], while Augustus was in his forty-second year [i.e., 3/2 B.C.]” (Commentary on Daniel 4:23:3). The Kalends was the first day of the month, and eight days before January 1 is December 25.
This is the earliest record we have of Jesus’ birth being December 25. It precedes by seventy years the time the Emperor Aurelian made Sol Invictus a Roman cult, and it precedes by a hundred and fifty years the earliest claimed reference to Sol Invictus being celebrated on December 25—that claim being based on the Chronography of A.D. 354.
So, it is possible the the Dec. 25th date was the date of his actual birth. It is certainly not out of the question like watchtower presents.
Excellent discussion on the topic here.