Coinfrog has got it right, In 1950 Milford H. Bolender published The United States Silver Dollars from 1794 to 1803, a reference book based on his own specialized collection of Bust dollars. He described and illustrated each variety known to him at the time and assigned (B) numbers to each coin. The book was extensively revised by noted collector, Jules Reiver, in 1988. A second reference book, Silver Dollars & Trade dollars
of the United States: A Complete Encyclopedia, Vol. One, authored in 1993 by Q. David Bowers and Mark Borckardt corrected and updated the Bolender book. Each known variety was assigned a (BB) number.
"Buy the Book Before You Buy the Coin" - Aaron R. Feldman - "And read it" - Me 2013! ANA
Life Member #3288 in good standing since 1982, EAC Member #6202, NBS Member, 2¢ variety collector.
See my want page: http://goccf.com/t/140440