GM Body/Floor Plugs
 

Several recent threads involve a search for GM floor drain plugs. I've noted a few different styles around the perimeter - both plain edge and notched edge, and these together with combinations of no holes, dimples (that look like punch marks), 2 holes, and 4 holes. Not to mention, dated and undated.
Anyone know if the different styles varied by era, supplier/assembly plant or by vehicle model?