Just got my PU Euro 5W-40 delivered from Amazon, I think the production date is December 2013. The bottles doesn't say they meet API SN, the label just says they meet or exceed SM.
I got some PU 5w-40 from a local auto store a month or so ago. It was dated Dec 2013 as well, and API SM. SOPUS has a lot of extra SM bottle labels sitting around that they're trying to burn through. And what's really inside the bottle - who knows?
My guess is the labels won't change until the new PurePlus 5w-40 comes out.
According to the spec sheet, the SN version has significantly lower Noack which some believe is an indication of a higher quality, more stable base oil.