To the best of my knowledge, the taxable CO2 figure is for each drivetrain (engine+transmission) in the basic trim. Weight of additional equipment is not considered, even though it does affect emissions.
So, you get a 1.4 170CV, and load it up with stuff, it still gets taxed at Band B because the lightest 170CV 1.4 car emits 134g/km. Yours mightn't, but the Revenue don't want to go into that level of detail.
Actually, because the percentage of VRT charged on the 120 is higher than for the 170, Alfa's margin on the 170 will be higher too... remember this when you go to trade in.
If there were changes to Bravo, it may have been that one of the European models was just over an Irish band threshold, and by stripping out some things they were able to squeeze it in.
(Incidentally, has anyone else noticed that you can't buy a "normal" Ford Focus with a petrol engine in this country anymore? only the 200bhp or ST are petrol powered.)