You probably hit bone socket on the opposite side of the buck with the second deer. There's no way you wouldn't penetrate a whitetail with that setup unless you hit something solid (not ribs). If you hit ribs, behind the leg on the fore side, you should have taken out both lungs and the deer wouldn't have went far, even though you didn't penetrate the far side.
As for the first shot in no man's land, that is all muscle where you hit and the deer may recover from that, so you can't compare that hit to one in the chest cavity, which will normally penetrate more easily.