Garen Q doesn't apply static shiv properly
If you have static shiv ready (at 100 stacks) before casting q and running to hit a target the static shiv proc goes off before it even has time to determine if you crit or not. This means static shiv will never crit in a situation where it was ready before you cast q. If the shiv becomes ready during your q auto attack animation however it will crit properly.
So in a more general explaination the static shiv procs at the start of the q animation and not the end when it knows if you crit or not. This also means you can kill someone with just the static shiv proc and still have the q bonus damage to kill someone else (though this is rare)
I know this isn't because it is an empowered auto because I went and tried it on wukong a game later.