Codes on Sellier & Bellot M1 Carbine Ammo

This is somewhat of a continuation from the previous thread on the M1 carbine corrosively primed ammo. That thread: http://forums.gunbroker.com/topic.asp?TOPIC_ID=536399

I was thinking that the modern production boxes for the Sellier & Bellot M1 ammo indicated current production, but when looking at the codes stamped on the inside flap of the boxes, I've begun to wonder if this could be old ammunition repackaged in new commercial boxes?

The two boxes I have out here (I threw away most of the ones I shot, so I'm not sure if these match the ones that have shown to be corrosive) are marked "19/ 48" and 19/ 55."

Could those numbers be dates? Was old ammo repackaged in new commercial boxes?