Another complication is the NPV of the base stocks - for example for the longest time XOM's website has not advertised GIII - are they using all of it - or most plus have contracts for the balance? They do have GI, GII+, PAO, mPAO, AN, and ester - so as both a consumer and seller - each would have a value with the company. Sticking with XOM - they have a long history of mixing various base fluids (since they make them all) - so Mobil and other majors can keep high performing lubes at a mainstream price point.
If it means so much to you - just pony up and buy Redline - it's "mostly" ester based ...