I have to agree, if we're going to be 100% authentic, the only way that's going to happen is to be a soldier from the Napoleonic Wars.
Am I doing the men I portray an injustice because of the shoes I have on my feet, no I am not. Do I look unauthentic because of it, not really no. If it's been authentic enough to parade in front of the queen, then it's authentic enough for most things. My baker rifle isn't authentic, for a start it's not even rifled, and secondly it's made in india, does that make it any less of a rifle? no, it looks as it should do, and does what it should do (i.e. shoots frenchies (sorry Mr_T!)
Authenticity takes you so far in your portrayal, if you're such a snob about it as some Napoleonic units are, you end up looking like a load of dicks on the battlefield, I'm sure Mr_T and co will agree with that (coughcough rifle units with belgic shakos).