There is some interesting material on the Univ of Durham CEM web site which parents might be interested in reading.
I think I'm correct in saying that the KE Grammar 11+ Exams are bespoke exams for the Foundation set by the CEM based on the GETINTU Framework.
The following is a quote from their web site:-
Every year the test content changes to reflect our ongoing research and development and to ensure the tests remain novel and engaging for the children who take them. There is little or no advantage to be gained from using commercially available test materials to prepare for these tests. As such we believe that they offer a fair assessment for all children, whatever their educational background, as far as this is possible. The tests are not language-free, however, and directly target proficient readers of English. It is our policy not to issue any practice materials.
The following link provides further information about the GETINTU Framework and the educational basis of the tests.
From what they are saying about the form of the tests it is quite consistent with the insider statement that the tests may change from year to year.
They also clearly do not like tutors and tutoring!
Hope this is of interest.