Fuel alone can account for a 5 mpg diff between ethanol content, summer/winter addatives, etc. Its my experience the Honda like humid air too for mpg.
Mines was made in March of 09 according to the drivers side door sticker and Ive heard the early ecus are not flashable.
That was something changed in the later models of the first and thereafter models and hte flash has something to do with the cvt as well as the "bettery charger" of the 12 volt side.
I could always get a late model ecu, then program it to my vin and keys, then Ill be back where I started where it cant be flashed since its vin related. I guess I could get a flashed ecu, then get the keys programmed to it. Not sure if programming of the vin to the ecu is just something for recording keeping purpose or if it actually plays a role in how everything interacts.
One of the things I liked about the crz is the fact it will asssist if needed and as soon as you lift it regens, so in other words it wont regen while accelerating, just when coasting when its low.