Three known varieties. Maybe this will help. I am not knowledgeable about all the VAM's out there. http://www.vamworld.com/1882+O+Over+S
You may want to read the information at this link as I believe that it would give you better understanding of this variety . http://www.nationalsilverdollarroundtable.org/an-analysis-of-the-1882-o-over-s-morgan-dollar/