I thought that the cord mentioned in the Iliad was more a plot-device or a hypothetical then some actual artifact with which Zeus is thought to have gained or enforced dominion. That’s why it’s “a cord” not “the cord” (assuming for a moment that Greek uses definite and indefinite articles, I actually have no idea if that’s true). Perhaps the later myth of Zeus and Nyx is a riff on, or allusion to, that older story from the Iliad.
