According to the JAMA report on the all meat experiment, Stefansson consumed ends of bones supplying about 100mg calcium daily (less than by Inuit). The report on the experiment states:
"The increased amount of tartar on Stefansson's teeth and the lack of evidence of lowered blood calcium offers an interesting field for speculation. There was no decreased density in roentgenograms of the hands at the end of the experiment when compared with the hand of a man on a general diet."
Testing only the hands with X-ray does not tell us whether he lost vertebral or trochanter bone; and X-rays don't have the ability to detect the small amount of bone density lost in one year.
In fact, the National Institute of Arthritis, Musculoskeletal, and Skin Diseases (NIAMS) has this to say about X-ray tests for bone density:
If you have back pain, your doctor may order an x ray of your spine to determine whether you have had a fracture. An x ray also may be appropriate if you have experienced a loss of height or a change in posture. However, because an x ray can detect bone loss only after 30 percent of the skeleton has been depleted, the presence of osteoporosis may be missed."
So the test used to evaluate effects of an all meat diet on Stefansson's bone density would only have detected loss of bone if he had lost 30 percent of his bone mass. Simply put, at the time of the experiment, they did not have a technology capable of detecting smaller yet significant changes in his bone mass.
Further, they don't report before and after X-rays of Stefansson, they report comparing Stefansson's hands to those of a man "on a general diet." Which can't tell us whether the diet had any impact on Stefansson's bones.
The failure of Stefansson's blood calcium to decline is not surprising, since body can prevent drops in blood calcium by extracting calcium from the bones and tissues. Low calcium in blood causes PTH release, which extracts calcium from bone to raise blood calcium to normal levels. Thus, on a calcium deficient diet, blood calcium will not go below normal until bone stores of calcium have been exhausted.
Stefansson reportedly had increased dental tartar, which indicates increased salivary calcium and phosphorus. What makes this happen?
This study showed that administration of PTH increases calcium and phosphorus in saliva: http://www.ncbi.nlm.nih.gov/pubmed/404157
Thus, we can surmise that Stefansson probably had increased PTH, which was probably resorbing bone to maintain normal blood calcium, simultaneously raising the calcium content of his saliva, producing increase in tartar. The calcium and phosphorus should stay in bones, not be deposited on the outside of teeth.
I also want to note that Stefansson consumed organ meats that supply vitamin C (brains, liver, etc). To that extent Stefansson did replicate an Inuit diet. He in fact made it very clear that to live on an all-meat diet requires replicating the Inuit diet in several important respects, including eating far more fat than protein, eating organs, etc.
As an experiment, I ate an all meat diet for more than one month. I ate ends of bones, but not every day, and liver once weekly. Within a few weeks, I developed severe muscle cramps indicative of mineral (primarily potassium) deficiencies. When I added vegetables and fruits back to my diet, the cramps diminished. This tells me that an all meat diet does not adequately provide me with potassium, for which I have to eat plants.