I asked the seller if there were any numbers printed in the hinge area. His reply was: "To the right hand side of the right hinge when opened the number 2919 is inscribed twice on the edge of the top and again on the base. Above the hinge stamped in ink is the number 5310. In two areas it is stamped on the inside cover in ink Brandis & Sons Inc. 754-758 Lexington Avenue, Brooklyn, New York."
I will leave it to others more experienced in this area to decide which number might be the Brandis number and which might be the NO number.