Hi Pip,
I haven't hunted in the USA, so I don't know your species very well. But I was born and raised in Africa, so I know the species there quite well.
I've also spent A LOT of time working on a safari operation, and from what MAJORITY of the American clients that I hunted with, said that the kill zone on African game is a lot lower and further forward than your American species.
On another note, you mentioned that most of the "way back" or "bad" shots shown on videos were recovered. Yes this is true in most cases, BUT what they probably don't mention on the video is that it took a team of 4 trackers, 1 PH, the client, and most likely a dog or two 3-4+ hours to recover the animal (say a Wilderbeest shot thru the liver). African game is VERY tough and a badly placed shot can easily result in a very long follow up or even loss of the animal!
Another thing, with all do respect to Kevin Robertson and his work, I don't like his recommended shot placement. For me personally, with all my experience hunting in Africa, I would NOT shoot the game where he recommends! I think that his books show a good anatomy of the game, but I wouldn't shoot it where he recommends. I personally believe that most of his shot recommendations are often too far back and high. Another book that I would recommend, if you can get hold of it in the USA, is "Shot Placement Pocket Field Guide" that is published by African Hunter Magazine. It's a really nice compact field anatomy guide for African game.
I hope that this has helped in some way. I hope you have a fun and successful hunt next year! Good luck!
Nigel