Originally Posted by flyerCO
If they re-route you on a partner (in this case they did) you get credit for the flight you took. If they had re-routed you on a non-partner (AA,UA,US,etc) you would be able to claim mileage for what you were supposed to fly on NW. To make it even better when flying on a non-partner you normally can also claim mileage in that airlines program.
This is correct. The only additional comment is that you usually have the option when re-booked on a partner of getting either your original miles/bonus/segments, OR the re-route miles/bonus/segments etc, but not both.
You were on a direct flight. You got basically the same miles/bonus/segments on the NW flight to CLE as you would have on the NW flight to CVG. You then got the additional miles/bonus on the DL flight. If you want to call NW I am sure they will give you the original mileage and take away the DL miles.