I believe that Shadar Haran is actually someone from one of the earliest books whose soul has been recycled. He is a very major player added relatively late in the game, so it makes some sense that he is not really new. However, since Shadar Haran is a Myrddraal, the Dark One may not be able to place a human soul in that body.

Further, to be granted such a position of power and authority, the individual would have to have been one of the Dark One's most faithful servants, perhaps even one who strove mightily to work his master's will, but was thwarted and killed by the accursed Rand al'Thor.