I notice that when I inhale something too hard through the nose that most of it lands way back in the throat (or whatever that area is called).
It still works this way but I don't think absorption is as quick or complete as it would be through the nasal membranes.
When you snort properly, the drug absorbs through the nasal membranes. When you snort too hard (or inhale through the mouth, as you are asking) The drug will coat the back of the throat and will enter the lungs.
So the drug will absorb through 3 ways with varying levels of speed/effectiveness: Some will absorb through the throat, Most will drip down into the stomach, and some will absorb in the lungs (similar to smoking/vaporizing). It won't be as effective as properly snorting since most of it will drip into the stomach.