I actually monitored this for the major I used to work for. It begins in the south (Texas of course) and works its way up the pipelines to the Northern peninsula. All tanks must be turned by May 1st. The only difference is the amount of butane(s) in the fuel. It is removed at the refinery, stored underground in vast caves under (slight) pressure until winter. As soon as RVP "time" is over, it gets pumped back out of those caves and added back into the low RVP tanks, making them "winter fuel".
A strange exercise for sure, but required by the EPA to limit summertime evaporation and vapor lock.
You don't hear too much about vapor lock these days, with the demise of carburetors and the pressurized fuel systems inherent to fuel injection, but it's still a thing.
Soooo, if you have some gas in cans that you bought over the winter, and your lawnmower has a hard time starting in the summer heat, now you know why.
Conversely, if you have an older car with a carb, that you filled up this winter, and it "floods" this spring you'll also know why.