Among the calibration people I've worked with, a "robust" open loop calibration is considered one where the short and long term fuel corrections are a multiplier of "1" once closed loop fuel is enabled, i.e., they're not doing anything to the open loop cals. Of course, with a car with that many miles, there could be some degradation in the air or fuel systems, such that closed loop fuel corrections have to compensate. And one never knows where there particular car ended up with normal part parameter specification. One other thing I might mention - the O2 sensors usually read lean during a misfire. All that extra oxygen, unconsumed by the unburnt fuel.