Turns out I had gone 274 miles!
So I was fairly pleased at this development, and then immediately fell into a spiral of self-doubt and sadness, as I don't really know what explains such good fortune here. Is it because of the duct tape over the lower vents of the Corolla's front bumper? Is it because I am driving more like a Granny now than ever? Is it because traffic has been kind to me and I haven't been tricked/trapped into many situations where I needed to speed up and slam on the brakes a lot?
I will know more information about this tank's mileage next week, as I'll probably refuel either Monday evening or Tuesday morning. But at this point, it's looking really good in support of the duct tape, even if it's just in my mind.