This is the way I understand it and this is what happened to me when Single Stack went permanent and they ran the archived classifiers en mass.
When the special match scores are turned in, 2 things are going to happen. First the initial classification where the best 4 of the most recent 6 will count.
So, we have 75,50,25 (Jun, Jul, Aug) and then the special match happened. Using the high to low sort, the 6 are 75,50,25,90,80,70. Dump the 25&50 you get 78.75% for the initial classification. So the shooter is now an A shooter. But there are a total of 9 classifiers on file so now you get the best 6 of the most recent 8. June (75) is out due to age. So you get 90,80,70,60,50,50 or 66.67%