> Regardless of the original contract, it's entirely appropriate for a vendor to tell the customer how to use any materials.

Utter nonsense. When the US built the Blackbird, it could only use titanium because of the heat involved in traveling at that speed. But they didn't have enough titanium in the US. So the the US created front companies to purchase titanium from the Soviet Union.

Do you think the US should have informed the Soviet Union what it wanted to do with the metal?

What does the customer informing the vendor have to do with the vendor informing the customer?

Your comparison seems backwards