I'm doing edexcel triple science too and your school may not be the same, but i done 3 controlled assesments ( 1 bio, 1 chem, 1 phy) and I will get 3 separate GCSE's - biology, chemistry and physics. Each will be made up of the 3 exams + the controlled assessment. e.g. B1, B2, B3 and the bio controlled assessment will make my biology grade. How have you found the core exams so far??
If you're doing triple then you'll be doing B1, B2, B3 and CAA for Biology and so on for Chemistry and Physics. People who do double do C1, B1, P1 and a CAA to make core science and again for additional science. However you can't do B3, C3, P3 and a CAA to make Extension science GCSE as Extension isn't a GCSE in its own right. Long story short, if you're doing the extension exams then you must be doing them as part of individual science GCSEs. You will get a GCSE each in Biology, Chemistry and Physics. Sorry for the long answer! Good luck with your exams xxx