To be honest as teachers we are in a no win situation here.
I had yr 11 and 13 groups for whom I had to supply CAGs for - I had to use all available evidence, therefore a good result on one mock was assessed against all other evidence i.e. class tests, homework, classwork etc as we had to provide the evidence for each CAG. If one of my students were displaying work at a grade 5 in classwork, homework, tests but pulled out a 7 in the mock because the weight of evidence was towards the lower grade then that's what I had to go with.
Our CAGs were then dept moderated so if 1 teacher had provided a lower grade than the evidence suggested this was discussed, opinions given and possible changes made (both up and down)
This was then passed to SLT who looked at all the grades, all the evidence, all the data and questioned any 'odd grades' (at this point the class teacher was out of the loop)
At this time schools were told that they could be asked to immediately provide evidence for the grades therefore any schools trying to play the system were taking a huge risk.
I know of 1 student in my school immediately wanting to appeal a CAG, trouble is for 18 months he had hardly done any work, homeworks missing, low test scores - all evidence pointed to this low grade with nothing to support his claims.
The one shinning light out of this is that as teachers we have the perfect sentence to say whenever a student thinks a piece of work doesn't matter "remember the class of 2020"!