As Chénier already mentioned, scout reports DO give more detailed information than can be otherwise acquired. If a foreign army was operating inside of a realm, I am sure that the realm would be actively scouting them and not simply rely on the information provided in the region details.
It only makes sense to me that there are networks upon networks of informants at work within the realms borders. As a prominent noble I would expect my staff to provide me with such information. Sure, all the little details of how all this information is gathered and distributed might be fuzzy, but that just leaves room for role playing how the information came into your hands.
One thing another thread made me think of, however, is that perhaps scout reports should also tell the movement of nobles without units. Even with an army of scouts you can't predict the movement of infils without units.
