That oil was a cheaper product of Ashland ( made Valvoline until 2017, now just a chemical company ). The oil was sold to various places and had the ratings for 1988 standards IIRC. Some brands did mark it for vehicles made before 1988 and was actually popular because of it's ZDDP content for older cars.
I don't remember who is bottling WM oil currently. FWIW, Walmart supplies bottles to various suppliers to meet their demands when it comes to automotive fluids. This is why sometimes the washer fluids are slightly different colors.. The oil in the containers now might not be the same as 6 months ago. A WM employee can find out manufacture by scanning the barcode