Yes I know war is messy and that surprise 20k men in the arse is a defeat and impressive to accomplish but there was more to war. Have you read the books or just being nitpicky?
I agree. Unfortunately war is really just about dull stuff, like logistics and management. There's no way those 20k men can get to the rear of the enemy without being given the order to do so, and the order being interpreted and implemented correctly, as well as ensuring all the soldiers have weapons and are supplied with ammunition, food, and equipment (such as that required to make camp and cook). Without sufficient organisation there is no way that enough men can be recruited and kept alive long enough to make a surprise attack.