That's amazing. Just about everything has improved since 2013, so if your battery is that good, every other battery out there should be better (assuming they've been taken care of). The couple of 2014 Leafs I tried had a lost 1-2 bars of battery life (out of 12? 14?). My current 3 year old Hyundai has yet to lose any range (knock on wood).
One thing about state of charge is that with some cars, like a Tesla, you can select a maximum above which not to charge (charging stops at say 85%). With others, like my Hyundai, I cannot set a maximum, but I assume there's a margin between the indicated 100% and the real 100%.
I wish all makers would think of the used market and include some kind of battery health indicator. It's hard to know how well a used battery has been treated. Leafs have health bars, but I don't about others. Mine doesn't, I don't know about others. Indicated EV range should be a required spec and filter criteria on Autotrader.