I average about 5.5 miles/kWh in my 2012. This is with 40 psi in the tires, no HVAC running, windows cracked, on flat roads with 35mph speed limits and limited stop lights. I use as much regenerative braking and cruise control as I can, but I don't do any crazy hypermileing techniques. My best mileage in a single kWh is 6.4 miles, but my best average trip was 6 miles/kWh (exceeded 40mph for about 5 miles on my trip which dropped my average like a stone). So, with my "small" 9.5-9.6 kWh (usable) battery, I can get around 52 miles on a charge on an average day this summer. My guess-o-meter reads 50 miles on a full charge every morning. If I had a 2013/'14 I could probably get about 56 miles on a charge with the slightly larger battery. A 2015 might be able to eek out 60 miles on a charge with it's even larger battery than the '13/'14, but as others have said it all depends on your driving style and the conditions you drive in. If you drive on the highway, there's no chance you hit 60 miles on a gen 1. Lots of hills or stop signs? It's not likely. Turn on the A/C or heat? Nope...
But to answer the original comment about a dealer installed software update to increase mileage... Nope, those have never been issued/offered. There have been updates and recalls on the 2013/14 cars for some ECU programming issues, but they don't increase the usable battery power in the pack. They just clean up some bugs in the system, but the battery can still only use the same 10.2-10.3kWh of its 16.5 kWh battery to drive the car.