Please refer to the Department for Education statement:
Here is a summary of the DfE statement:
Where exams taken in the same series are scheduled for the same day, the best result will continue to count. Schools will need to think carefully about whether this is in the best interests of their pupils. The Department for Education will continue to collect data on entry patterns, and will share that data at a school level with Ofsted. In cases where exams are scheduled for different days, even if they are in the same series, only the first entry will count in the tables. In cases where exams are taken in different series, only the first entry will count in the tables. The only exception to this rule would be for candidates who took their first exam before 29 September 2013.
Only exams taken before the end of the candidate’s Key Stage 4 will count towards the performance tables.