Ride Description doesn't match ride report

I choose London 8 because the route description says there will be an 850-foot climb. But every time I ride it, I complete the mileage, the game displays a “route completed” message…and my ride report says the total ascent was 750 feet (actually Garmin Connect says it was 748 ft., the Zwift companion says 750). Why doesn’t the ride report match the ride description?