What was explained to me:
If the ingot was heated for rolling, that would not be melting, that would be processing - the steel did not actually melt to combine ingredients together. The cert cannot legitimately state "melted in USA"; it can state "manufactured in USA". (You already know this, Hg - this is more for the sake of others)
If a foreign origin pig iron or basic steel ingot was melted and alloys, or modifiers, were added in a USA furnace, it is melted in USA That is where the steel becomes the final steel alloy it ends up as. The cert won't say where each came from.
This makes sense when you consider that many of the elements in steel today comes from foreign lands - some of those do not exist in the USA. (Much of the iron ore came from Canada).
So you could think of it this way - the flour came from Canada, the sugar came from Haiti, the vanilla came from Spain, the eggs were from Mexico but the ingredients were mixed and cookies were baked in the USA. So they are USA cookies.
If the cookies were baked in a foreign country, but packaged in USA, they are still foreign baked cookies; and sold in...(no- I'd better not go there!)