Hi AG2012
Namur/Namen used date letters.
Rosenberg is a good free reference book but indeed outdated.
Reference; L'orfèvrerie en Belgique /Silver in Belgium 1500-1800 by Piet Baudouin, Pierre Colman and Dorsan Goethals. Herewith an image of page 186 examples of guild hallmarks date marks. See number 81 Namur;
Regards,
Peter