One thing that may not be obvious unless you've dug into it, is that the i3's user visible SOC is not the 'real' SOC of the batteries...it is the normally usable range and BMW has a buffer built in at both the top and the bottom of the range. Someone said the upper buffer is there so there's room for regen if you leave with a full battery. SO, it's possible if your trip started on the top of a hill, you could get more power into the battery than it had when the EVSE and the car said it was full. Don't know if that's the full truth, but it at least sounds plausible. The bottom end buffer is for several reasons...batteries don't like to be discharged flat, and if there isn't at least some charge there, the logic to run the recharging cycle has to go through a different path to get some back before it can fully function and begin to use the full EVSE output. I don't remember the exact numbers, but it appears there's about a 5% buffer at each end of the SOC that is usable under normal conditions.
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)