The only point I would add is that the very same principle of self-validation applies to continued belief in Biblical "prophecies in general. How, otherwise, could a book that ends with the expressed wish "Come Lord Jesus" still be believed a good 2,000 years after the all the end-times urgency? Answer: Self validation by explaining away why it hasn't yet happened but it soon will.
JWs are only a specific case of a more general problem with Bibilcal prophecies.