Austro-Hungarian marks were extensively revised in 1866 with the introduction of the "Dianakopf" mark; the assay office code letters were revised at the same time. "B" was the code letter for Prague from 1807 until 1866; it was changed to "C" in 1866, which it remained until the dissolution of the Austro-Hungarian Empire after World War I.
The code letters in the link you provide are applicable
only for the marks in use 1866-1922. I have, in fact, done some research into these codes. Here is a link to a chart I have created, which I believe to be the most accurate and complete listing of
Austro-Hungarian Assay Office Codes, 1866-1922.
But the "B" code on the ladle in this thread - dated 1819 - is definitely for Prague. If members are interested, I can compose a similar chart of the code letters in use 1807-1866, but I would ask your patience in doing so.