I don't think premium is, at least not usually. I think they add all the additives and get the octanes of those where they're supposed to be at the refinery. But, yes, mid grade is just a blend of high and low grades.
Two grades of gas come from the refinery, or distributor's rack. They do have the specified additives, per company. Mid-grade is a blend via your site's computer system, both turbines running at once.
Love the Nova pic. My dad’s first 3 cars where Novas! A 62, 69, and a 77. (Don’t know what he was thinking! ).
My Dad had two Chevys - a '68 Bel Air and a 74 Chevelle. The Bel Air was fantastic, tough as nails, but the Chevelle was a total lemon... It wasn't long and Dad went and replaced with with a 73 Gran Torino.
That's the one! Except it was a dark blue metallic color. Rode smooth as a cloud, and more than once Dad looked down at the speedometer and exclaimed "Whoa!"... without noticing, he was doing 80 mph on a 60 mph highway (or it was Mom who said, "Hey! Lead foot!"). One didn't notice the speed and the 302 under the hood was really quiet and smooth running. We kept that one for a long time.
With family in AZ, I looked on a map and found Gripe is 170 miles and three hours east of Phoenix in what looks like very remote country. Looks like you could view a Gila Monster there. My brother and I saw a very large one being unkind to a train in the 1959 movie The Giant Gila Monster. It's since become a family standard for bad movies.