Based on what I have read, the serial # is a pretty good indication. Not all SCC-1As had the insert included in the packaging to indicate that the card was one of the newer ones with the extra voices. I could do the test but do not wish to go to the trouble.
Thats your choice. I look at your auction (and so will most people) and see an scc-1 and bid accordingly. However, if you could gurantee the extra voices you would bring in more money...