These updates to the modelling are done to make the projections more accurate.
It's not just Canada doing them. Some of them come from calculations about the warming potential of various greenhouse gases—not just CO2, but the other ones as well. Ms. Leach can explain that in greater detail.
To answer your last question, I don't know, for each time they've modelled it, whether it's brought them closer or further. The point isn't to remodel to make it further or closer; it's to make it more accurate.