Using GOM values would be really inaccurate. Which driving mode was the car in? How had it been driven during the previous 18 miles? What was the ambient temperature?
I'd put my money on the Idaho National Labs' tests of 4 new 2014 i3 BEV's. INL has sophisticated equipment that can measure battery pack capacity better than any i3 driver can. Three lost 7.5% of their battery pack capacity within 12k miles and 15 months of normal usage. The other was driven for only 4k miles and 3 months during which time it lost 3.4% of its capacity. Of course, these i3's all had 60 Ah battery packs which seem much more prone to capacity loss than 94 Ah and 120 Ah battery packs.
2019 BMW i3 Imperial Blue Metallic, Giga World, Tech + Driving Assist, Heat Pump, 428 Wheels
[FOR SALE] 2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging