I have two George III pennies in my collection. One is dated 1806 and is in Very Fine condition; the other is dated 1807 and is in Almost Fine - Fair condition. I was intending to offer the latter for sale but I am concerned that it may be a forgery. Although it looks the same as the earlier coin, it only weighs 18.1 grams. The earlier coin weighs 18.9 grams, which is the correct amount. Could the difference be attributable to greater wear or some other factor?