I have tanned deer, Elk, otter Beaver and a host of others with brain method, acid, alum, chrome solution,and soft soap, the non-brain methods use a saltdown to aid the removal of the flesh and open the pores to take the tan, I am most certain that if you salt cure a hide of any type then soften and dry it into a useable form that it will go to pieces very shortly with repeated exposure to water. In order to make "leather" that will survive being wet for any period of time a chemical change must occur that salt alone does not produce, acid, chrome solution and the smoking after braintanning will do this, I suspect the methods of Boone may have been salting for short term storage and fleshing then Tawing (softening by manipulation)to create a soft product, by smoking afterwards, the garment may have lasted a while without it or another source of chemical change in the skin fibers it would be very short lived in all but the driest climates.the salt itself will wash out as does alum when this is used to Taw hides.