I did the one additional paper which is Helicopter P of F in order to upgrade ATPL(A) theory to ATPL(H).
You can do this so long as you have taken the exam by Mar 06.
I had to speak to the head of ground examinations to get this answer.
If you let it go by the 3 years you will have to do the bridging papers which would obviously suck!!
Revise the Bristol Feedback and you'll have no problems.
Good Luck