not sure i understand what you want to know, but here goes:
early models made with imported parts were better than the majority of other imported SA at the time, and even better than many SA made here.
recent USFA "all-american" SA are among of the very finest in the world.
you asked: "Why then would one want the later USFA US parts revolvers over the earlier ones...?" a better question would be why anyone would prefer an earlier model. i sure don't.