I would recommend "United States Large Cents 1793-1794" by William C. ("Bill") Noyes as a good starting point if you have more than a passing interest in the 1793. It is more up-to-date and much more in-depth than Sheldon's early efforts.
The unique NC-5:
http://images.goldbergauctions.com/...ite=1&lot=97Somewhat obscure provenance before 1946 when it was donated to the ANS Cabinet. Prior to that, Virgil Brand owned it at one point. Flowing Hair type, vine and bars edge.
EAC graded 8 by Bland; sold for $2,185 in October 2001. Currently the coin resides in a PCGS AU58 holder. Ex: Mouhtouris, Bland, ANS Cabinet
One of the two NC-6:
http://images.goldbergauctions.com/...ite=1&lot=25The variety was not discovered until 1978. This is the second of the two examples.
Graded EAC 4, choice, by both Noyes and Bland. Last sold in September 2009 for $40,250. Liberty Cap type, lettered edge.
Former EAC President Dan Holmes, who passed away in 2016, had all of the 1793 varieties at one point save for the lone NC-5. The aforementioned Brand Cabinet had all known varieties except for the NC-6 which had not yet been discovered at the time.
Both of the above varieties are scarcer than the "Strawberry Leaf" of which 4 are currently known. Mr. Holmes owned two of those four, a corroded PCGS G4/EAC 4, which sold for a mere $370k, and a PCGS Fair 2/EAC 3 graded example with nicer surfaces but more wear which sold for $389k.
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