Indeedly do! I'll post the outcome of that investigation shortly.
Anyone remotely interested in the history of the Orcs (which is everyone of age, in a world defined by their invasion) has atleast some understanding that the orcs were in league with demons, or slaves to demons, or something like that; and characters with an adventurer's bent (all PCs) would know more. How much more is a bit of a spitball; but I think it's fair to say all our PC's know that the orcs were under a demon-blood pact which faded after the invasion ended, leading to the Lethargy.