NEC3 contracts do not split out “prevention events” as a separate item or process. The equivalent of a prevention event is covered as one of the standard 19 reasons for which a Contractor can claim a compensation event (60.1(19)).
60.1(19) is meant for events that stops the Contractor from completing the works (not delays) that would have had such a small chance of occurring etc.
I think this follows on from a previously asked question and the answer will be the same here. Who’s risk will depend on what your contract says. Between the contract wording and the Works Information it should have made it clear who’s responsibility/risk this particular item is. Just because it was not under your direct control does not mean that it is not your risk. This is why you need to be very clear as to what you are signing up to.
As with any compensation event you need to find a reason within clause 60.1 that makes it a valid compensation event, and if you cant find one it means it isn’t one. The only good news here is that with option C this will in effect be a shared risk. Even if it is not a compensation event, it will not be a disallowed cost either. Therefore you will be able to claim the money spent but not raise the target. (if you can prove it is a compensation event you can obviously claim the money AND raise the target).