I think the issue is not the 1914 date by itself, but the way they tied it to expectations for so long through their explanation of the 'generations.' The idea, for a long time, was that there was a growing urgency as we got farther from that year, because there was a clear limit to the amount of time left. That helped with recruiting and with keeping the rank and file in line, because people will hedge their bets-- if the end is that close, why not stay in a bit longer to be sure?
They've modified the explanation, but they really should have just said 'look, we have new light and it says that 1914 is correct but the generation teaching doesn't apply to the modern age. So we know the end is near, but we cannot say how near.' That kind of kills the sense of urgency you get from having a specific number or numbers, but their approach (overlapping generations) is likely to turn away more people than just admitting that they were... mistaken.
Sometimes you must take the honest approach and hope for the best. Because if you keep peddling dishonest teachings that get more and more convoluted and unconvincing, you are still killing off your religion, but in a way that people will never forget and use as a cautionary tale.