Example:
    Date    Field   DesiredNew
    1/9/1994    D   C
    1/8/1994    D   C
    1/7/1994    D   C
    1/6/1994    C   B
    1/5/1994    B   A
    1/4/1994    B   A
    1/3/1994    B   A
    1/2/1994    A
    1/1/1994    A