There is an online archive of the early watchtowers/golden age/awakes. In 1916 there was a Questions from the Readers entry regarding the baptizing of people after 1914. Since the followers were told that the "rapture" was going to occur in 1914, that was the cut off date to get baptized. 1914 having come and gone without anyone going to heaven, the query was what to do about people wanting to get baptized now?
So it was a definite date promoted by the WT. It's plain from the after effects.