A quick question - without the opportunity to examine the source code, would it be possible to confirm airworthiness of the aircraft before entry into service?
All the standards I'm aware of would require access to the source code to assure software of the level of integrity required for flight control and avionics. That doesn't mean that it can't be assured if the US witholds the source code, just that the partners won't be able to assure it themselves independently.
It does mean that they'll have us over a barrel for future upgrades and no doubt they'll demand expensive annual maintenance fees because they know there's no possibility of competition.