Lets try a different way of looking at grades versus competitions.
A grading doesn't predict the future.
A grading determines which competition a shooter qualifies to compete in (but the shooter could compete in a higher grade comp). So a past average of an A means the shooter can only compete in A (or AA) but not B or C.
If you look at the competitions for the summer GP season and you see one or more individuals scoring A or even AA as an average but they are graded in B or C then you would not expect them to qualify for B or C next season. Regardless of how they perform over the off-season (i.e. Winter).
Entirely hypothetical and no individual in mind or even considered.
A shooter has a super GP season and wins B or C but the results would put that shooter in A just taking in to account BFTA competitions. Said shooter then decides he/she is bored using the successful rig and spends the winter trying out a different rifle, scope, pellets, rail height, sitting position and after many rounds of B (or even C) scores decides enough is enough and hits the For Sale section and goes back to what worked last year. (sound like anyone we know? ) The outcome would be a summer Grade dropping down below an A to a B or even C (said shooter lives close to more than one region and cares nothing for fuel costs and shoots a graded event every weekend - my hypothetical shooter so I can make s**t up).
So in the above scenario the shooter for the next season has a distorted grade but only because regional scores are included, it would not impact the grade if that grade was based on the previous BFTA rounds (there aren't any in the Winter). The shooter would now only qualify to shoot in the A grade competitions and all is well. Shooter uses the tried and tested, scores brilliantly and wins A and moves up to AA.
Some shooters care damn all for the grades and focus on performing brilliantly at events that matter to them - Worlds, Euros, whatever.
So - past scores for a given series determines future qualification for the next series.
BFTA Secretary 2012-2014
CSFTA Secretary 2014-2016