Ron Guth:
The XXX edge is one of four edge varieties found on 1809 Half Dollars. These include: XXX edge, IIIII edge, plain edge, and the so-called "normal" edge (with "a pseudo engraved in front of FIFTY" - per Overton). Several varieties comprise the XXX edge: O-101, O-102, O-108a, and O-110. Curiously, different die states of the same variety can have different edges. For example, O-102 is found with the XXX edge, but O-102a is found with a plain edge. Similarly, O-108 has a IIIII edge, but O-108a has a XXX edge. Be sure to examine the edges of your 1809 Half Dollars carefully - it is quite possible that you could discover an unknown edge usage where it is least expected.