Why are so many American nibs not marked 14K?

Unlike most other nations, the US has never had a law that all gold articles be officially tested for content and hallmarked. The top American penmakers clearly felt that imprinting their names on their nibs was sufficient guarantee of quality. Generic nibs, however, were always stamped with the gold content ("Warranted 14K"), as were nibs on pens destined for export.

Solid gold overlays were almost always marked; jewelers will often assure you that an unmarked gold filled pen is solid gold, but this is almost always because the testing methods are applied to the solid gold topmost layer of the laminate.