Originally Posted by
channa
DL/NW didn't have it because they didn't refer to themselves as sDL and sNW.
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It is more that what the crews are referring themselves as. After the DL/NW merger, the resulting corporate entity's name was Delta Air Lines Inc. After the CO/UA merger the corporate entity's name is United Continental Holdings Inc. That's part of the division here. It implies that there are separate United assets and Continental assets.