Whilst at the stage 2 (out of 2) process, I chatted to a Lady from HR, we discussed the new 3 stage process, and during that conversation she informed me that in the new process you would only have to resit from the stage that you failed from, i.e. once you have passed the tests you don't need to do them again... One would imagine this is only from the new process onwards, but you never know.
Cheers,
James.