I recently got the following email from a regular MileCalc user:
I am a Delta flight attendant (flight Leader actually) who relies on your service before every trip ... the mileage is usually dead on with what's on the Delta paperwork handed to me. With one exception……DTW-DEN. You say 1223. My Paperwork says 1235. Could you by any chance be using the mileage to the old Stapleton Airport?The distance between DTW and Denver International Airport (39° 51′ 42″ N, 104° 40′ 23″ W) is 1223 miles. The distance between DTW and Stapleton International Airport (39° 46′ 45.32″ N, 104° 52′ 54.62″ W), which closed almost twenty years ago, is 1235.
The Delta SkyMiles calculation is erroneously using the now-defunct airport. Is this good or bad for mile collectors? Well, that depends on the leg. Depending on the location of the airport you're flying to (or coming from), you may gain or lose up to 12 miles.