Also, how does 70 and 95 average to 92??
They don't average the percentiles, they look at how common or rare your final score combination is. It's like sports: someone who can score 20 points per game in the NBA isnt rare. Someone who can rebound 10 rebounds a game isn't that rare either. Someone who can both score 20 points and grab 10 rebounds? That is extremely rare...
Is it possible that the percentiles may change as more people take the test?
No, they don't adjust the percentiles after the test, yours is locked in once you receive the official report. I think they compare it to previous scores only.