I am flying PDX-DFW-MSY and return in June and recently noticed my flgith number changed. After further inquiry, I also noted slightly altered arrival and departure times as well as an aircraft change. DL swapped a 737-800 for an MD-90 PDX-DFW. What is the reason for this? The reason I am asking, is I had specifically booked seat 18A-exit row, yet now I am am stuck 12A on the MD-90 and the flgiht is now full. I know the aircraft have similar capacity, so what was the point?
I know this is kind of an oddball question but any light that can be shed on this would eb appreciated