Ok, sounds like they weren't banned officially until 1951, but was looked down on in many JW circles. Perhaps it was similar to the attitude toward higher education? Perhaps this attitude started taking off in the 1940s? The reports of Witnesses celebrating birthdays in the Watchtower magazine mostly came from the beginning of the decade. Below is the only passage in which birthdays are connotated with something negative in the WT of the 1940s. This is the one I referred to at the beginning of this thread. I imagine many could have read into this Christmas article as being a condemnation of birthdays as well:
Look high and low in the Christian writings of Jesus’ apostles and thier companions, and you will not find once the word "Christmas", neither the word "mass". Not only is the date of Jesus’ birth not given anywhere for the purpose of having it celebrated, but the only birthday celebration mentioned is that of the adulterous King herod, whose step-daughter Salome danced to make the celebration "merry", yes. merry by having the head of the forerunner of Christ, namely, the head of John the Baptist chopped off (See Matthew 14:6-12, Mark 6 21-29). Even Origen of Alexandria (A. D. 185-254), who is celebrated as one of the "early church fathers", was sharp enough to see the point, so that he stated that "in the Scriptures sinners alone, not saints celebrate their birthday". Jesus Christ nowhere instructed his disciples to celebrate his human birthday on either the legitimate day or any fictitious date and for religionists to engage in such a celebration on a religious fixed date, which date if furthermore sacred to a heathen false god, is a case of adding to the Word of God. Concerning this it is written, at Proverbs 30:5,6 "Every word of God is pure--he is a shield unto them that put their trust in him. Add thou not unto his words, lest he reprove thee, and thou be found a liar." (The Watchtower, November 15, 1942, p. 349)
Again, as Leolaia pointed out from a later Christmas article, the main argument against Christmas is that Jesus' followers were not instructed to celebrate his birthday, and the fact that it's celebrated on a pagan date makes it even worse. The info brought out about birthdays being celebrated by sinners in the scriptures is treated more as a side issue, and there is no condemnation of Christmas on the basis of it being a birthday celebration.