Back in the 80s Shell brought out their Syn-arctic 0W30 motor oil. It was semi-synthetic, meaning about 50% synthetic to meet the very cold starting needs in the North. I was priced midway between regular mineral and full synthetic, which not commonly available at this time.
The present definition of blend or semi-synthetic is all over the map, and of dubious value if it is a 5W30 or heavier.