1813 BD-2 is one of two die varieties of 1813 identified by researchers Walter Breen, Harry W. Bass, Jr., and John Dannreuther. This is the rarer of the two varieties -- once rated Rarity 6 it is now considered a Rarity 4, with approximately 20-30 known. The two varieties share the same obverse, thus the varieties are distinguished by minor differences on the reverse.
The best example of this variety is the PCGS MS66+ example once owned by the Garretts (T. Harrison, Robert, and John Work) and D. Brent Pogue.