First, although the 10104 designation appears in the usual reference books, such as Fusi, for US Giulietta Spiders, every US Giulietta Spider I have ever seen (including mine) has a "10103" ID tag on the firewall. I seem to recall a thread about this on the 750/101 List a few years ago, and no one had ever seen a "10104" tag.
With respect to wiring differences, 101 Euro Giulietta and Giulia Spiders had side-marker lights on the front fenders (but not 750 Euro Giulietta Spiders), while the US cars did not. The same for Sprints; I'm often accused of having add-on side-marker lights on my '59 101 Sprint, but they are correct since it is a Euro car.
For both Euro and US 101 Giulietta Spiders, a wiring change did occur in July 1961 when the cigar lighter was added, although I'm not sure when this made it into the wiring diagram.
On a final point, having re-wired both my Spider and Sprint, there is total confusion between the wiring diagrams and the cars concerning green versus gray wires.