-well the 12s are original boot design they are narrower and usually run a size up. i wear a 9 shoe but a 10 boot.
-the 13s fit more true to size and a bit wider so a 9 is a 9.
i believe these both are compatible with all system bindings 2011-14
the 14 boots are very similar to the 13s wide and true to size, they have a thinner outsole and heel while being completely flat on the outsole, so they're only compatible with the 14 bindings.