I pulled a 5181682AG/5181677AI for a 2012 WK2 6.4. The 2015's receive a change to one of the CAT's, but not the other. So yes, for this application, the catalysts appear unchanged.
Yes, which supports what I've said.
Maybe for this application it is less of a concern, but in principle, all engines consume some amount of oil and catalyst poisoning is a cumulative effect over time. Generally speaking, the more "catalyst unfriendly" components there are in an oil, the shorter the catalyst life will be. Whether that means 200k vs. 250K, I don't know, but for someone who lives in a state that pretty much requires OE catalysts, I prefer to use oils that will give my catalysts the best chance of living the longest possible life. Replacing the catalysts at high mileage could effectively "total" a vehicle.
Sure, so then one has to consider the consumption levels. The OE has to work with the "worst case scenario" projection and the cat lasting the emissions warranty and the cheapest possible oil that meets the API requirements (which aren't very stringent).
I prefer an oil that isn't compromised on wear prevention just because a rule was written to limit phosphorous so that the cheapest possible garbage that can make it through the API approval process and gets consumed in an engine drinking 1 quart every thousand miles doesn't kill its cat within the warranty period. To each their own of course.
Some of this was driven by GPF's, but not always. Porsche primarily went to C40 (instead of A40) due to the GPF matter. VW has been specifying 504.00 for their Atlas models and those do not have a GPF. Honestly, I am not convinced that the older full SAPS oils provide "significantly better" wear protection for applications where they were not originally specified. Their starting points may be higher, but this may not translate to better real-world performance for all applications.
One of the things reduced was also TBN (detergents), as I'm sure you recall, which affected serviceable life of the fluid with higher sulphur fuels. Full SAPS is "no limits"; there aren't constraints made on phosphorous levels, so it will be very much optimized for wear prevention. Phosphorous had to be reduced a bit in the lower SAPS formulas, but it isn't a huge reduction. It's phosphorous we are talking about because that's what primarily poisons catalysts and why the API limits are so low.
Keep in mind that SAPS levels are not only defined by the P/Zn content - there are other components in an oil that can increase the SA levels. For the longest time, Amsoil had a disclaimer in their Signature Series PDS that said "Fortified with detergents that exceed the dexos1 Gen 2 sulfated ash specification." All of the VOA's posted of Signature Series show a fairly standard SP/Dexos 1 add pack, but they have modestly higher levels of the other elements (compared to most oils).
We are sort of melding two different things here. SAPS levels are primarily a concern for Euro marques, that's the genesis of the mid, low and full SAPS labelling. This does not put wildly restrictive limits on phosphorous, as I demonstrated in my reply to you. 900ppm of phosphorous is not uncommon in an ESP oil. This was primarily implemented to protect DPF and GPF's.
The API specifically limits phosphorous to 600-800ppm in anything xW-30 and below for catalyst protection, that's far more restrictive than the Euro stuff, despite their (the Euros) prolific use of GPF's. But of course the API has historically been much more lax on things like volatility, which increases the likelihood of oil making its way into the exhaust, and subsequently, phosphorous.
While yes, SAPS is more than just phosphorous, phosphorous is what most are concerned about, or are most concerned about, with regards to catalyst poisoning. But again, that requires it getting to the catalyst in the first place.
