Doing some research on calendars, in particular our calendar, you will find that there is no accurate date . For instance a pope took two weeks out just to match up with some of catholic dogma, not sure what it was. Some experts say our calendar could be off as much as 30 years.
Another problem with coming up with 1914 is that russell counted his days from 606/607 up to our day not counting for the difference in the length of years. He just counted years as in our calendar. He also did not allow for leap years as far as I can tell. And everyone knows that he forgot about the zero year thing. People that believe in numerology seem to forget alot of those little things.
I am definitely not an expert on this, but I have always thought it would be impossible to come up with the exact date.
There are hundreds of dates throughout time that some nut has said would be the end of the world, or the start or end of something or another, they were never correct of course. It has been proven over and over again that man has no insight into the future. Jesus said no one knows the day or the hour, and he was so correct.
I still believe this all had to do with the destruction of Jerusalem. Even Titus, after looking over the massive and total destruction of the city in disbelief, said (paraphrased) 'surely god had a hand in the destruction of this great city, for I certainly had no control of it myself.' The temple had even been destroyed after his explicit orders not to harm it. He wanted it to stand as a testimony to the power of rome.