Note the rim on the reverse? (not the edge, but the area between the outside devices and the edge. That should also be showing on the obverse, but is now missing because it was removed from the coin by a mechanical means. There is an raised area on all planchets that help create this rim.

Note the first example of a blank. No edge is present. When it is ran through the upset mill, then it looks like the second example called a planchet. When the coin is struck the rim is the distance between the edge of the die and the collar that makes the coin round.
If the rim/upset is present on one side and not the other it was removed. Altered.
PSD