Your shot likely included one of the two:

1) Portal Vein which is a vein that takes blood into the liver from hindend. This vein is probably the size of your thumb if not larger.

2) Descending Aorta which is a artery that takes blood from the heart back to the back half of the body. This runs directly under the spine(it is also very large) which several have talked about.

Both will bleed/kill a deer very quickly.

As far as a generic liver shot....If you don't get one of the major hepatic vessels (liver veins) or the portal vein (going into liver from body) or inferior vena cava (leaving liver and going to heart) then it will likely bea slower kill (which some have eluded to).

Hope this helps.