Soon will work forever. It has worked for full human lifespans of several generations of JWs so far, so no reason it won't keep working.Slimboyfat - Thats not true. Until 1995 JWs always had a specific timeframe to work with (1914, 1925, 1975, the generation). This "very soon" vagueness is relatively new territory, me it's proving difficult to sustain.
A specific date is not required for "soon" to work. Look at Christianity. 79% of Americans still believe in Jesus Second Coming to Earth, and 79% think it will be in their lifetime, and they don't have the strong eschatology of JWs. http://www.pewresearch.org/daily-number/the-second-coming-of-jesus/
BESTY Now the 20 somethings and recent converts have only ever known 'soon' - thats the difference I'm trying to explore.
It is an interesting question. However, I am not sure that there is a large difference between the number of born ins that leave now, and that left in the 1970's or 80's. Franz claimed it was 2/3, which is still what it seems to be today.
I think that it is harder to get new converts without the urgency, and for them "soon" does not cut it. As with Jeffro's graph, there was a spike in growth prior to the specific date of 1975, which also occurred prior to 1914 and 1925, and even in the 1980's with the final push regarding any logical meaning of the generation.