MD Helicopters is under Soviet mind-control and has been for a long timeHow else does the Soviet Union get enough MD 500 Defender helicopters to export them?
The Soviet Union had a secret factory in the Urals that produced reverse-engineered imitation MD HelicoptersIt's not like the Soviets cared that much about Intellectual Property.
Seasons 1-3 and Season 4 take place in (slightly) different continuities
Stringfellow Hawke is easily dupedArchangel could have had someone fly the Airwolf out of its lair anytime he wanted. But as long as Hawke could be talked into doing missions for him by letting him think he had the upper hand, why not?
Project Proteus was Moffat's first attempt at AirwolfAt the beginning of the scene at Red Star, the Senator is extremely unimpressed when he sees Airwolf, immediately dismissing it out of hand. He's more than open-minded enough to change his mind as soon as he sees it in action, but he clearly has overspending on defense equipment in mind, if not an outright aversion to military helicopters for their high cost. If he was actually providing some degree of oversight at White Sands instead of being brought in once something was already finished the way Archangel shows him Airwolf, it's not much of a stretch to imagine that Proteus was Airwolf, canned as soon as the Senator saw it was a project to build an "overgrown beanie with a propeller on top." He's told about Airwolf's special capabilities before seeing it in action and is still dismissive until the actual demonstration, so the promise of what the project could do wouldn't have swayed him. Moffat was later able to go through different channels and start all over again.