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Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,413
This sort of flight number is used for such additional sections.
The other obvious alternative when one notices a one time only flight is that it's a charter for a sports team.