Don't know what book you are referring to, but I applaud both the advice and your interest in it. I did JMT SoBo last year and and had no problem carrying 12 days food from my last resup. If your food pack is reasonably nutrient dense, there is no reason why you can't get 12 days food (16 lbs) into a bearcan, plus what you can carry for a day out of resup: easily 13 days food for 11-12 days south of VVR. To paraphrase Cap't Quint: I'll never resup at MTR again.
