It is more accurate if you track mileage for the entire OCI. ...
Yes, definitely so (for the formula that uses "mpg"). In fact, that's a thinly disguised version of one of my pet ideas, that for any particular oil+vehicle combination, change intervals would be better defined if based on total fuel consumed since the previous change, instead of simply on distance traveled. In that case, the other terms in the formula are essentially constants, but variations in idle time, weather, short trips, towing, etc. are reflected in the fuel used, hence in mpg.
term overly favors large, low-specific-power engines (e.g., pre-1950 tech), methinks.