Clipped corners were very common on CDVs, I believe they were clipped to fit into photo albums. I have no idea if this is related -- there's a 30-year gap between the height of CDVs' popularity and t-206 -- but it seems too similar to be a coincidence.
relevant examples:
http://legendaryauctions.com/1863_jo...lot154257.aspx
http://www.robertedwardauctions.com/...2010/1143.html