If I shoot an expanding bullet solidly into the body of a large game animal such that the bullet will travel the near full width of the body, the bullet impacts at a velocity exceeding the bullet manufacturer's advertised minimum velocity for expansion, and the bullet doesn't expand - that meets my definition of a expanding bullet failing to expand. I don't care if the bullet impacts the body in the guts, the bladder, the stomach, the liver, the ribs, the shoulders, the hams or the neck. My personal expectation is that the bullet will expand, providing it impacts above the manufacturers specified minimum expansion velocity. If it doesn't, the bullet failed me. I didn't fail the bullet.
On average, I think animals and people are 80% water by weight. Water offers plenty of resistance to bullets to cause expansion. If a bullet won't expand when it impacts water, I don't wanna use it. If an expanding hunting bullet has to impact bone in order to expand, I expect the manufacturer of that bullet to inform its customers of that restriction.