An approximate 700,800, 900 and 1,000 days in service might not be a bad idea to mark on the calendar, if it's not too much trouble, to check trend analysis.
Sat March 11th, 2017 700
July 20th, 2017 800
I will probably try to take data about once a week and at as many different battery levels as possible so that there is more data to judge by. There is a lot of uncertainty in these calculations, so having a good point cloud should help to bring out the real trend.
If you are getting 4 miles /kwh on average, take it down to 4 miles left, as an experiment, and see what it indicates left % on your phone, and what it all calculates out to for capacity.
Getting the car down to very low SOC actually takes some effort. We only got down to 8% because I forgot to plug the car in after my wife had an unusually busy day driving around. I took the car the next day and found a place to charge it at lunchtime, just enough for the rest of my day of driving. Just before that charge was the 8% remaining, so it represented two days of driving. I would expect that a longer period of use between charges would introduce more uncertainty in the calculation.