I don't know to which specific KE you are referring, but last year an appeal being granted led to one extra in a class as Camp Hill Girls. I assume from this that they had already reached their maximum before appeals were heard, then after this point no other children dropped out so they remained one extra.
I can see circumstances where an appeal was granted, then a place became vacant at King Edward Handsworth (which usually has the most movement) at a later date and the school might then decide that, as the appellant already brought them over number, they would not offer this place out.
In this way the appellant gained a place that otherwise would have gone to next on waiting list.
I don't see how any of this, however, would help you argue your case. In fact, you could argue that, if this is what happens (which I'm sure it does), then the child winning the appeal effectively gains a place which otherwise would be going to a child who gained a higher score and this is disputably unfair to the child on the waiting list.
I am not sure challenging something like this is going to help. I think your best bet would be to concentrate on proving that your child underperformed due to circumstances surrounding the test (distractions in the room, problems at home etc.)