As I've mentioned before, the numbers in French marks correspond to the official départemental numbers of each particular regime; the assay office numbers used in the first three post-revolutionary series of marks – First Republic (1798-1809), Empire (1809-1819), and Restauration (1819-1838) – are all different, and you must make sure that you are checking the appropriate table of assay office/département numbers corresponding to the particular series of marks. (Tardy gives only the 1819-1813 table.)
Département 50 in 1798/1809 was Loiret (not Haute Marne), and its assay office in Orléans. I checked Nicole Verlet-Réaubourg's Orfèvres d'Orléans and, yes, it shows that the mark on your tastevin is that of Louis Sionnest (1743-1811; master 1769) of Orléans.
Hope this helps!