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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: 102,617
I've seen this happen after a schedule or aircraft change. DL starts with an empty seat map and it can take at least a few hours for everyone to be assigned a seat again.
IMO trying to grab a better seat in the interim will not result in the seat you pick sticking, but this is based on only a couple data points. YMMV.