The best source of information on this date is the book "The Flowing Hair Silver Dollars of 1794 - An Historical and Population Census Study" by Martin A. Logies. Mr. Logies documented the appearances of over 125 different 1794 Silver Dollars along with their auction pedigrees and other pertinent information. This information is crucial to anyone contemplating the purchase of a 1794 Silver Dollar, since many of the coins are impaired and/or or repaired.
A single pair of dies accounts for all known examples of this date. Many examples show adjustment marks on one or both sides, where excess metal was filed from the planchet before striking. At least one example (the PCGS SP-66) shows both adjustment marks plus traces of a silver plug (which was added to the center of the coin to raise the weight of the planchet to the statutory requirement).
At some point in the striking process, the dies shifted and their faces were no longer parallel to each other. This resulted in weakness on the left side of the obverse and the corresponding area of the reverse. Only a very few 1794 Silver Dollars exhibit what can be called anywhere near a full strike.
Two copper patterns exist of this date, both unique. The first pattern shows all of the design elements except for the obverse stars (Judd 18). The second (Judd 19) is a well-struck die trial (presently in the National Numismatic Collection at the Smithsonian Institution). Judd 18 and Judd 19 have different obverse dies, but share a common reverse. Both the obverse and reverse dies of Judd 19 were later used to make the regular 1794 Silver Dollars.
Sources and/or recommended reading: "Walter Breen's Complete Encyclopedia of U.S. and Colonial Coins" by Walter Breen
Independent Coin Grading Company advertisement, Numismatic News, October 3, 2000, page 21
"The Flowing Hair Silver Dollars of 1794 - An Historical and Population Census Study" by Martin A. Logies
William Strickland Collection - Charles Winn (husband of Priscilla Strickland, son-in-law and cousin of William Strickland), Rowland Winn, 1st Baron St. Oswald of Nostell - Rowland Winn, 2nd Baron St. Oswald of Nostell - Rowland George Winn, 3rd Baron St. Oswald of Nostell - Rowland Denys Guy Winn, Major the Lord St. Oswald, M.C. - Christie, Manson, and Woods 10/1964:138 - Jacque C. (Mrs. Alfred) Ostheimer Collection, sold privately on 0/29/1969 - Superior - Edwards Huntington Metcalf Collection - Superior 10/1973:1209 - Jonathon Hefferlin - Bowers & Ruddy 1/1975:371 - Julian Leidman - Michael Kirzner - Bowers & Ruddy - Phil Herres (DollarTowne) - Leon Hendrickson (SilverTowne), by sale, via John Dannreuther, January 1983 - Jimmy Hayes Collection - Stack's 10/1985:72 - David Akers - D. Brent Pogue Collection - Stack's/Bowers & Sotheby's 9/2015:2041, $4,993,750
F.C.C. Boyd Collection - Numismatic Gallery "World's Greatest Collection" 1/1945,1 - Numismatic Gallery 8/1949:140 - Beverly Hills Stamp & Coin Shop (Abe Kosoff & Max Justus) FPL 8/1/1957 - Numismatic Gallery 8/1958:1678 - James Kelly, sold privately in 1967 - Lelan Rogers - Stack's 11/1995:1315 (as Gem Brilliant Uncirculated), $577,500 - Stellar Collection
Lord St. Oswald Collection - Christie’s 10/1964 - Norweb Collection - Bowers & Merena 11/1988:3741, $242,000
Virgil Brand Collection - B. Max Mehl, sold privately in the 1930s - F.C.C. Boyd Collection (duplicate), sold privately by Numismatic Gallery at the time of the "World's Greatest Collection" sale - Stack's FPL No. 47 (1950) - B.M. Eubanks - Quality Sales 9/1973:464 - Abner Kreisberg Corporation 10/1978:633 - Bowers & Ruddy's FPL No. 41 (1981) - Steve Ivy 10/1983:3769 - Bowers & Merena 5/1992:1300 - Jeff Isaac - The Cardinal Collection Educational Foundation, and displayed as part of the Cardinal Collection of Early Dollars at the 2001, 2002 and 2004 ANA Conventions - American Numismatic Rarities 6/2005:5 - Stack’s/Bowers 8/2010:1005, $1,207,500