Curious about this…

I have just bought a second Traction – a Normale, this time(and I know I’m going to regret it when my wife finds out…) and looking at the Carte Gris that came with it I notice that it is described as an ’11 SIE B’ and I’m wondering whether there is any significance in the ‘ SIE’. Does it indicate anything or is it just a French Typo which I understand happens fairly regularly. Initially I thought it might be a shortened form of SerIE. Anyway, does anyone have any ideas?