These seem to be the allocation profiles for Surrey secondary schools for September 2018 (page updated on May 2nd, according to the website):
www.surreycc.gov.uk/__data/assets/pdf_file/0009/158949/Secondary-allocation-figures-September-2018-V2.pdf
George Abbot School
- LAC & PLAC. 2. Exceptional social/medical need. 3. Siblings at the time of admission. 4. Children of staff who have been employed by the school for more
than two years at the time of application. 5. Children for whom the school is the nearest to their home address. 6 Any other applicant.
Criterion 1 = 1, Criterion 2 = 3, Criterion 3 = 147, Criterion 4 = 2, Criterion 5 = 143, Distance = 6.594km, Criterion 6 = 0, SEN/EHCP = 4
Offered 300
Guildford County
School
- LAC & PLAC. 2. Exceptional circumstances. 3. Siblings at the time of admission. 4. Children of staff who have been employed at the school for more than two
years. 5. Distance to school.
Criterion 1 = 3, Criterion 2 = 0, Criterion 3 = 66, Criterion 4 = 3, Criterion 5 = 104, Distance = 1.802km, SEN/EHCP = 4
Interestingly, George Abbot's first what one might call 'general' criterion is not 'distance' per se, but 'Children for whom the school is the nearest to their home address'. So if there is another school closer to home than GA, the applicant would presumably fall into Category 6 - under which criterion no offers have been made for this year.
Schools can't 'keep back' places - if there are places available for all who apply, then all who apply must be offered a place. If more apply (wherever they ranked the school on their CAF) than there are places, then all applicants must be ranked by the school according to its oversubscription criteria
However, not all those who can be offered a place will actually have put that school in a position on their CAF above any other school which can also offer them a place. So on the initial run of offers, not all places may be filled, but late applicants (moving into area after the cut-off date for change of address / people changing preferences etc) will then be offered the places still available - again, all of them if there are enough places, but once there is only one place left and more than one applicant, the child who fits into the highest oversubscription category / ranks highest on the the break if I'm the same category, will get the place.