An arrow on the ground should be re -shot. An arrow showing damage has no way of saying that it was damagedat that target or by the arrow on the ground. On a long target with poor lighting there is no way that anyone can say that one arrow hit another unless there is only one other person shooting in the group. Rules are made to cover every possibility as can be determined by people using a standard that covers as many shooters as possible. A mixed group of people may not agree on whether or not damage was caused at the target or even during previouslyshooting together.