Shadow bolsters have been used mostly for aesthetics since the mid-1800's - there are a lot of fine old Sheffield MOP, ivory, tortoise shell, and horn knives that have shadow bolsters (or tip bolsters - much the same - with tiny slivers of bolsters at each end of the knife -- the pivot pins still go thru the scale material directly).
However, the whole shadow construction goes way back -- usually using a pivot pin that goes thru washers on the outside of each of the scales and is peened over them (same basic concept that Tony has elaborated). Look at the construction of lots of old French clasp style folders made of horn or antler or wood. The old friction folders also use this sort of construction.
I've heard that Tony says the construction used in his shadow knives is actually stronger than an equivalent bolstered knife. Makes sense - with solid micarta or G10 type scales, and the reinforced pivot area, the whole knife essentially becomes one solid structure. With bolsters, there is always the thinner, discontinuous area where the bolster becomes the liner and the separate structure of the scales.
However, as to the origin of the terms "shadow bolster" and thus "shadow pattern", I'll have to turn that over to someone else. Why did they call no bolsters at all shadow bolsters? I know they used the term shadow this way back in the 1800's, but I don't know why.
-- Dwight