A. W. Browning
Sources of the edited annotations in this edition of Browning's classic work are as follows:
EPC = Walter Breen's Encyclopedia of U.S. and Colonial Proof Coins 1722-1977. New York: FCI Press, July 1977, updated by the author and reprinted by Bowers and Merena Galleries, 1989.
G: (+lot number) = Superior Galleries, Clarke E. Gilhousen (et al) auction, Oct. 1-4, 1973. (Descriptions by Breen; the coins were mostly from the Dr. Charles L. Ruby Collection.)
LM: (+ date, lot number) = Lester Merkin auction, 1965-72, separately identified by date; descriptions by Breen.
NEQ = Walter Breen, "Notes on Early Quarter Dollars," Numismatic Scrapbook Magazine, XX, 2: 137-146 (Feb. 1954).
NN: (+ serial between 33 and 61 + lot number) = Netherlands auctions, 1951-63, separately indentified; descriptions mostly by Breen.
Other sources (aside from attribution numbers) are cited separately.