If you evaluate various Product Data Sheets (PDS) for non synthetic SN plus PCMOs, there is a common theme in the descriptions stating the oils are synthetic blends. This holds true for all major brands. What is not disclosed in the PDSs are the percentages and the Group of the synthetic base stock used in the formulations. I expect oil blenders are using the minimum amount of Group III base stock required for them to meet API SN plus approval in combination with modifications to the DI package. SN plus PCMO formulations are using lower levels of calcium and increased levels of magnesium in the detergency package to combat LSPI.
Super Tech 5W20 and 5W30 conventional PCMOs meet SN plus requirements; so, these oils may very well be synthetic blends albeit with low levels of Group III base stock. Also, I reviewed the PDS for Super Tech 5W30 from WD, and it uses less calcium and more magnesium than the previous SN formulation as verified by the VOA posted on the PQIA website.