Note that the bottom cup/race is round vs squarish as on the 1971 Bianchi above. Prior to about 1961, Bianchis with integrated headsets had a round bottom cup/race, and
a top lock nut with two holes rather than four. Top tier vs cheepo? Or maybe newest/latest/greatest vs somewhat obsolete? I'm way further down this rabbit hole than I've ever been
researching my mystery Bianchi, and that's sayin' something as I'm pretty OCD about these things...