Again, not semantics. Or rather, semantics in the sense that the two signifiers are not interchangeable, and signify different things. International first class exists and is very different from North American ("domestic") first class. It's also considerably more expensive than business class, and is for the least price-sensitive customers, who appreciate caviar, apron transfers, in-flight showers, and rubber ducks. The fact that there is no direct first class service from ATL to AMS is beside the point.
Also, the top deck of 747s is not always for the highest level of service. Back many years ago, AF had non-smoking economy up there. And LH has business class up there, and first in the nose (where it's quieter).