First, is there anything Union can do to prevent this event? What exactly means that Union needs closing Richmond? How strong army have to be? Is it enough to sneak a brigade or there is requirement in terms of minimum number of elements? How close that force needs to be to city itself: in adjacent regions or only what counts is direct assault on very city?
Second, I really think events like this one have to be documented somewhere. Either in manual, scenario design notes or inside the game itself. It is not funny when your NM suddenly drops significantly during PBEM game because of some event which players didn't know about. Player should be informed about it in advance (for example in similar way like it is informed that he is not able to form corps before march 1862). In this case, I figured out why my NM dropped -10 NM only by searching old AACW forums.
