I had a very similar experience buying a '14 Spark at the end of the year last year. The predicted mileage is based on recent driving, and things like heating temperature. I also see around 55mi of range in colder weather, but on warmer days, or if I preheat the cabin while it's plugged in I see...
I'm also a new member, also with a used '14 spark EV! I got mine in December with 30k miles on it. I'm so impressed by this little micro car. I was worried I wouldn't be able to make it home from the dealership 60 miles away, but I managed to get home with 11 miles of range left! I got 5 mi/kWh...