Caught speeding at 85 in a 70 zone (probationary period). What percentage of the time will you receive a letter?

How much % comes a letter?

99.1%

There are 2 scenarios known to me in which a flasher triggers, but in the end no letter comes.

1. If it is unclear who has triggered this can happen for example in multi-lane roads, then sometimes 2 cars are depicted on the photo that does not clearly indicate which of the cars has triggered the flasher.
2. Calibration photos. When a flasher is set up in a new place, calibration photos must first be made. During this phase, the flasher triggers for each car, regardless of its speed. You usually see a few people with laptop and warning vest standing next to the flasher.

and when one comes as high will be the punishment

40-50€, depending on whether it was inside or outside a village.

And how much tolerance is actually deducted?

3km/h of what the flasher measured.

But since your speedometer is not a precision instrument, the flasher will have measured less than it was on your speedometer.