Ninety days worth of flying may be more indicative of someone's flying pattern over an entire year than thirty or sixty days, but I really think it's a stretch to say that there is any meaningful relevance to that period over the long term. This is precisely for the point that oklAAhoma raises - that is, one can hit PLT via challenge with concentrated activity during a short period (or even in the span of 48 hours) that may or may not repeat itself.

Let's consider, as an example, the fact that I logged nearly 13k Q-points during a 30-day period between July 28 and August 27. Using your logic, that is an indicator that I should have had no problem getting to EXP. This is not the case, however - not only am I not close to EXP, I'm requalifying for PLT via segments this year, not points or miles. In fact, I'm going to only have about 42k Q-points this year.

I have no doubt that, for some people, the 3-month period is an indicator of consistent future activity. By and large, though, I don't think that three months is really any more indicative than two months, one month, or even one weekend - because the other nine months (or longer) have too much potential to be simply random in comparison.

Mike