I phoned the contact number on the CAA website, and was eventually put through to someone who was fairly helpful.
I'm afraid I didn't ask them what you are supposed to do if you have not yet finished the exams. If you find out, please post here because there are some other students at my club who are in this position.
The examiner at my club is as baffled as anyone else - he has not been issued with any new papers or been notified of any changes.
I think the best thing to if you are caught between syllabuses is to phone the CAA and try to get a straight answer out of them.