At least in the U.S. Midwest, most stations have three tanks, one for each grade, no mixing. (I know some in the Northeast do mixing, Sunoco was famous for that. Some very new stations have more than three, sometimes six, usually for diesel, E15, and E85.) The Meridian Pipeline terminates into a tanker farm about 300M from my local bike path, I ride by all the time. Rail cars carry the ethanol in, and it's blended at "the rack" where the tanker fills up. Ethanol can't be put in a pipeline because it absorbs water like crazy (yet another reason to avoid it.)
When I took that photo, the tanker driver happened to be there unloading fuel, and I asked him some questions. The short answer, for V-Power, that particular station is the only Shell around here getting 91E0; all the other local Shells have 93E10. The only reason I can think of, that station is about 500M from boat ramps, and boaters know better than to buy ethanol. If that station didn't have one E0 grade, boaters would fill up elsewhere, probably the BP that's 7 KM south.
Another factoid, many independent stations in the upper Midwest (e.g., Kwik Trip) used to have a detergent package that met Top Tier detergent requirements (notably more than EPA requirements.) That was really convenient, especially in western Wisconsin where major oil co. stations are rare. Back in November of 2021, the Top Tier stickers started disappearing from the independent's pumps. There is reportedly a supply chain issue in getting the detergents, and nobody has seen when they'll be back. Third party companies make the additive packages, e.g., Lubrizol, BASF, et al. BASF reportedly makes BP's "Ultimate" additive for them in the U.S.
So in the meantime, I'm back to Shell, even though that station is about 20 KM farther. V-Power also claims to have friction reducers, anti-corrosion properties, and wear reducers, in addition to better detergent. Top Tier covers just detergents.
One more trivia point, Scuderia Ferrari found that going to E10 in the 2022 F1 specs meant that their V-Power lost 20 HP due to lower fuel density/BTUs. That doesn't sound like much, but in F1 where everything counts, it was a problem. For a street car, E10 drops BTUs about 4%.