Darn it I spent an hour creating a nice long descriptive reply, and then the cat pushed the back button and it is gone. I may see what I can do later once I get into the shop (Where I have another cat that like to lay on my keyboard as I try to write responses.)
Brief response, there is only one rare variety of chain cent NC-1, there are only two specimens known. The S-1 Ameri variety is popular in excess of it's rarity. (All the S- numbered chain cents 1-4 are of roughly equal rarity, around R-3+ to 4)
The best way to learn the varieties? Go here, copy the images of lots 1, and 3-6. (click on the image of lot 1, that will take you to the large images) Print them out so you can lay them next to each other and can look from one to the other looking at the differences. (One thing to not there are only two chain cent reverse dies. S-1 uses the Ameri die and all of the others use the other reverse die. Another thing to know is S-1 and S-2 use the same obv die. Third clue each of the obv dies can be identified even in low grade by the shape of the truncation of the bust, although NC-1 and S-3 are very similar.) More later.
http://images.goldbergauctions.com/...ter=1&page=1Since the NC-1 in the previous link is so worn, here is an image of the other specimen from the ANS collection
