Sure one-way trips count! They may not be as meaningful but it's still 56+ mpg over an extended distance (which was by no means a one-way trip out of the mountains or something like that). I was just driving down the coast of Maine and NH. I've gotten high mpg on the way up that trip too but that was early in my ownership of the car and wasn't as high as this--mid-40s though at least. But it's not a trip I do very often, so I don't exactly have ready round-trip stats--and I'm certainly not going to do it repeatedly to use a tank for precise results! Hell I can't even get that for just commuting to/from work, since by the time I refill it's guaranteed I'll have to do errands, too. So for anybody not doing a single trip 100% of the time, you pretty much get the numbers you can where you can, far as I'm concerned, hehe.

I don't know the exact location of my refill but estimating from the distance home, I'll guess Wells till I can verify. Wells, ME has allegedly an elevation of 69 feet. My town allegedly has an elevation of 12 feet. I'm pretty sure change in elevation was not a significant factor in my FE for this driving segment.