Yes, and our students do Core Science GCSE in year 9. However, we do have a Core Science GCSE group in year 10 as well, to allow flexibility between courses. It's complicated and I would rather we did a 2 year KS4 to be honest!
Any student joining year 10 this year for most subjects won't be able to take CAs until the year that they take the linear exams (although a CA year runs from May to May, so they could take it at the very end of the previous academic year - does that make sense?).