No, peter only assumes that there *is* a rate.  

Regardless of what the rate is, if it is any value for which there exists *any fixed central tendency*, tail emission is *evenually* non inflationary.

But you are correct about the other two things:

1. If people are improving custody faster than 1/(N(t)*P) than tail emission can still be inflationary.  This seems far-fetched, imo.

2. The rate will be somewhat stochastic ("black swan envets").  Plausible (popular wallet loses keys in coding error), but also... "true no matter what".  And not really relevant to tail-emission  being non-inflationary.   Over a long enough time period, even these events can be factored into a fixed central tendency.   Even if it's 100 years, etc.