The 1906 revisions of Banc D'Epreuves Des Armes a Feu De Liege are here
https://books.google.com/books?id=5fxGAQAAMAAJ&pg=PA53&lpg
Scroll down to p. 77 and it shows the stylized lion smokeless proof so the gun should date thereafter
The font of 'EXPRESS' shown is different
The pressure to which Nitro Express are proved is not shown.