The Euro approvals are typically significantly more demanding than the API ones, which is why Euro lubes oft lag on getting more recent API ones and some of them never even bother getting them. The API limits on additives has resulted in many xW-30 lubes not progressing beyond API SL (if they carry the API approval at all), which isn't a big deal, since none of the Euro marques call for API approvals in the first place.
The foundation for the Euro approvals are ACEA, upon which most of the OEM approvals are based, with their own tests, limits...etc.
If you watched the recent Engineering Explained video that featured some testing information from XOM, you'll notice that with API SP, the reduced the viscosity increase due to oxidation limit from 150% to 100%, while Mobil limits themselves to 10% for M1 and 5% for M1 EP. That's the kind of chasm that can exist between the API testing limits, and higher tier oils. Ergo, it's not surprising that a formula wouldn't require any changes to move on to SP from SN Plus if it already met more demanding OEM approvals in the first place. Mobil has often been way ahead of the curve in that regard, but that may also be the case for this lubricant, being a Euro-style 0w-40, it may have required no changes to meet SP. It may also have failed A40 if Porsche updated the test protocol, but that would have zero bearing on the updated API approval.
I'm still unsure why you didn't just pick-up M1 0w-40, which, when on sale, is roughly the same price and has a laundry list of active approvals.