Took a round trip between BWI<-->DTW<-->SEA Feb 2nd. The mileage for SEA-DTW-BWI legs has not shown up nearly 6 weeks after the trip. Submitting request for mileage credit requires the ticket number, which I did not have handy. I finally found my BP's and the e-mail from NW e-ticket receipt e-mail. I put in the ticket number and here is the response I got from Delta's website.
Delta has all the information, but their useless software cannot retrieve useful information from the data it already has.

All segments have been processed. Refer to mileage credit details below.

• Mileage Activity Date Flight Class Flown/Paid Description of Mileage Credit Medallion Qualifying Miles Code
• 02Feb2010 Designated Operated Miles Seg
• 02Feb2010 DL 2311 DL 2311 V/K BWI - DTW 500 1 1,000
• 02Feb2010 DL 2201 DL 2201 V/K DTW - SEA 1,927 1 3,854
• 02Feb2010 DL 2240 DL 2240 V/K SEA - DTW O
• 02Feb2010 DL 2384 DL 2384 V/K DTW - BWI

O - Duplicate origin or destination.
Firstly, the message is meaningless. Anyone with any common sense would not word a message thus. Delta programmers don;t seem to know that on a round trip itinerary the outbound destination is going to be the same as the inbound origin. And on an round trip itinerary with the same layover cities, the origin for each segment on the outbound legs will become destination for the inbound leg and vice versa.

Delta keeps making excuses that the glitches are due to integration etc etc. while the reality is, at least in this case, it's due to stupidity and incompetence.