I was perusing the FC seat maps as part of my routine in sizing up my chances for upgrade when I noticed that the fare class listed for purchase was "R2PBF". It was my impression that R was purely an upgrade bucket.

When I did this for previous trips, and even the same flights 2 days ago, the fares were in "P". The fare has dropped from approx $2500 to approx $1300 for a first class fare.

My theory is NW responded to Delta's SimpliFares by using the R to be a "deep discount" FC fare bucket.

Any thoughts?