The 'north' 'south' divide you mention isn't the case (or at least not that I am aware of). Those sitting on a single day are Out of County Applicants, which is entirely different. You may live in Kent buy if your LEA isn't KCC then you are not 'in', but 'out'.... All very confusing!
As for if they are fair, I didn't consider them to be on DS3 but for DS1 and DS2 they passed so wasn't fussed either way
The LA have to find some method of 'selection' and given the 'access for all' opportunities available it can't be by teacher assessment, because the teacher may have an ulterior motive to put a particular child forward.
I do agree that there should be a 'Kent Test' but strongly feel it should be on a level playing field, and that the LA have a duty to advise all parents that while they don't recommend tutoring, many parents do this for their DC. Then parents could make an informed choice, instead of living in a bubble having been told by the teacher it wasn't necessary. (although it didn't escape my attention that DS3's former Y6 teacher is now considering doing extra tuition out of school to boost his income, which makes me feel a wally for believing his 'standard' advise when he knows tutoring is the norm and I thought nobody was doing it