I was 50 miles short on the other half of One Pass (Mileage Plus) and had a flight that hadnt posted (500 miles). I called MP and asked about the flight and mentioned that I was short 50 miles. They looked at the account and told me not to worry, the miles would probably post in a few days but I had already 'been prequalified" to 1K for next year. Lots of variables, CO vs UA, Im a multiyear 1K and MM and I fly a fair amount of higher level coach fares. But I would be stunned if they didnt bump you. If you want no chance though, time for a short flight.