Higher quality viscosity modifiers do more than help the lube resist thinning, they can also contribute to the lubes ability to suspend & disperse contaminants and keep deposits from forming. That will not show up on a UOA. That will not show up on a PDS. Only Chevron/Oronite knows this.
A lot of things don't appear on a VOA/UOA, like some esters are actually good solvents and capable of dissolving varnish. (im not saying Chevron uses esters, maybe they do... maybe they don't, you'd have to get them to disclose that)