The way that GCSE grades are calculated varies for each subject and exam format but, generally, results are determined by the total number of marks obtained in an exam paper. Grade boundaries vary depending on the subject and the exam board. There are five boards used across England, Wales ...
I agree the exam system isn't an accurate reflection of whether someone is an independent thinker, but nor is it just regurgitating facts. There's nothing wrong with spreading GCSEs over 3 years if that works better, and active recall during revision is the best way to make things stick...