I'm assuming that all topics are on the exam until exam boards specify in January. Whole topics won't be committed, we just know what will be on the exam. eg: Biology AQA has 8 units but in each of them, they are divided up into further sections so the Responding to Change (unit 6) topic has survival and response (receptors/IAA/taxis/kinesis), nervous coordination and homeostasis. But the exam might only ask about homeostasis so exam boards say that this section is in the exam.
But again, for subjects like sciences and maths it won't be a large benefit as the papers are far too synoptic.