Based on WT history of repeated false prophecies, here is the way these things seem to develop:
1. Someone connects unrelated Bible verses and comes up with a date for the end.
2. This date is "confirmed" by outside information, such as pyramid measurements.
3. They share this "hidden knowledge" with others.
4. They develop a following of people who are excited to be the only ones on earth who understand "the deep things of God."
5. They promote the date.
6. People laugh them to scorn.
7. The faithful cry "persecution" and wait expectantly.
8. As the date approaches, they get more and more excited.
9. When the date is imminent, leaders get worried and start to hedge their bets through cautionary language.
10. When the date comes and goes, they come up with some explanation (Adam-Eve creation gap, no year 0, etc.) and set a new date in the near future.
11. When the later date goes by, they announce that they are done with setting dates.
12. After several years go by, they lose followers are forced to decide whether to disband or start over.
13. They set a new date and attract new followers who aren't aware of their previous failures.
14. The cycle repeats.