1. I think it’s late Octobrt usually. They change blends 12-15 times during the winter. The amount of butane in gas is essentially constantly changing through the winter season.
2. I don’t think it changes. If it does it’s going to be very minimal. I read somewhere in CA their 91 non-oxygenated, non-ethanol goes from a 7 RVP to a 6.9
3. I don’t think it matters on something like a 2-stroke auger, especially if you’re using 91 non-oxygenated, non-ethanol gas. I wouldn’t worry about it. I’ve got a strikemaster with the Solo engine and I’ve never had any issues starting it in eight years and I’ve ran some absolutely horrid gas through it. It still started on the first or second pull and ran great.