Originally Posted by themicah
Even worse, assuming both legs are on the same equipment, I'm pretty sure the SAME seat (i.e., 2A, 4B, etc.) has to be free on both legs, since I don't think the computer can assign you to different seats numbers on the two legs of the "direct" flight. You might find a GA who can override that on the battlefield, but I don't think EUA will.
While that's true, if NW provides "R" bucket availability for CLT-DTW-IND as a through flight, their systems will provide seats for it. It's built into their logic. So even though the FC cabin for DTW-IND may show 4 seats available but NW is willing to sell 6, that usually means 2 seats are reserved for CLT-DTW-IND as a through flight and they are holding two particular seats for through pax. Of course, this is not an indication of "R" seats for the through flights.
e.g. NW212 runs LGA-DTW-SEA, I've taken it rarely but never had a problem upgrading it at the 5/6 day window.
-RM