Also.. that "5" is smaller than any other numeral compared to the numbers on the date. A dropped element would be the same size.
For your information - From the website Chris provided http://www.error-ref.com/struck-through_dropped_filling
The image is somewhat blurred but all I see is post strike damage. I believe your mind is "seeing" a 5 in the random damage on the coin.
Well, my mind is definitely not seeing the number 5 randomly showing haha. It's there, but like Chris and many has pointed out, the "5" is much smaller compared to the date numbers. If you looked at the other pictures I later posted, I've circled the area where the "5" is located. Someone did a real good job making the "5" but they used the wrong number as well as size to make it look like an error.