Well, it kind of makes sense, lore-wise, I think. After the banner was taken one of the Sturgians (if I recall) snapped it over his knee and threw it on the ground.
Likely at that point it was discarded and forgotten - but that means there are two part of the shaft, and one banner itself - my presumption of the three 'pieces'. After the battle bandits and looters would come through and root around the bodies for whatever they could find. Lo and behold - "Oy, Boss, I found a neat stick - got a lil' dragon on it, ey?"
And there you go...bandits took off with the two halves of the pole and our good doctor got the third piece from another person who was there and raided it out.