I think there is also substantial room for error when judging an animal’s exact orientation to us. What someone perceived as ‘perfectly broadside’ could have actually been a bit more of a quartering angle than they realized. I have observing this myself in shots on an elk that I perceived as broadside, when in fact upon skinning the bull it was clearly evident that there was a slight quartering away orientation to the first shot wound path, resulting in the 178 ELDX from a .308 ending up primarily in the brisket. Little, if any, of that bullet affected the vitals, and follow-up shots were necessary.
My point is, at what degree of rotation around the vertical axis of an animal are we judging the transition from broadside to quartering? I’m sure we can all judge a 45 degree rotation around the vertical axis, but how about 20-30 degrees? 15 degrees? Unless you can always get a good view of the offside leg stance, or visually line up the neck and spine, I think there is a lot of room for error.