I don't think it is in dispute what the foreign government said and the letter too from the ambassador is authentic. So for the NSC to take cognizance of this is fine but the real issue is, did this foreign government go beyond and aid/fund the locals to subvert the then PTI government?
I think we need to see it from that standpoint. The response to the statements of the US official was a demarche condemning the USG's interference in the internal matters of the country. Anything beyond that will require proof that a foreign government did indeed aid the local politicians financially or through some other mechanisms.
How would the courts and even the establishment make that case that the US support was indeed given to the opposition?
AM, agreed that the statements made by the US diplomat were indeed stated and our ambassador and also the military attache relayed the same back. However, the issue is beyond it being real, i.e. what did the actual threats translate to on the ground? Did money change hands from outside to inside? Is that the factual case to make the NCV void? I am unclear what the PTI could ask for except the more general ask for new elections.
Unless people are utterly stupid, the ambassador's narrative cannot be any different than what PMIK has already reported which resulted in a demarche. However, for the NCV to be voided, real proof of foreign funding and collusion will be needed. That obviously is like finding a needle in the haystack.