You're mixing up the fare basis code with the fare class, the two are different. In most cases, the fare class is the first letter of the fare basis code, but this does not have to be the case. In the fare rules, you will see the fare class that corresponds to the fare basis code. If that is F, you will get the COS bonus.

That's what I've been saying all along. These "UP" fares that are not "B" or "Y" in the fare basis will not earn the COS bonus.

I think I'm going to stop now. I thought I made it pretty clear earlier on, but apparently not.

I've been on M fares that have the F fare bucket in the fare rules. I thought I made it pretty clear earlier on, but apparently not.

United does this, too. The have QUAUP fares that pull from the A fare class, which results in the COS bonus. This is not unique to NW.

As usual, Schmutz is dead on. I have done the MBR2F fares and did not receive the COS bonus EQM or RDM. Anyone feel free to correct me, but I believe that the "logic" of the fare is that it books into in my example "M" class. By magic only NW understands (:D ), you are immediately upgraded to the FC cabin. Consider it akin to EUA. Ride in FC get credit for applicable coach bought. Since, "M" class does not get any COS bonus, no COS bonus is credited. Alternatively, the "Y-UP" or the "B-UP" type fare gets you the EQM COS kicker but no RDM COS kicker because "Y" class and "B" class get the EQM COS but no RDM COS.:)

Then I've been lucky. I've booked these fares several times DCA-SEA and have gotten the COS bonuses. The "class paid" and "class flown" was definitely F on my statement even though the fare basis was MA2F. This may depend on the market, as the MA2F fares DCA-SEA typically match AS's full First class fare DCA-SEA.

And that there be the issue. :)

On nearly all of the NW "UP" fares, it always shows something like "F/M" or "F/V" for the "class flown/class paid" on our account statements. Perhaps in a few select markets a M-fare will show up as "F/F", but I think it's awfully rare and perhaps you really have been lucky...or it's a mistake. But that's certainly not how all, or even most, of the "UP" fares work on NW. Other airlines are different.

Here's a twist on this: Our corporate travel office booked an F fare (with Fxxxx fare basis) for me but was seated me in Y on one leg since First was full. You do *not* get the 1,000 upgrade guarantee in this scenario. So, they will sell you a First class fare, seat you in Coach if First is full and then not give you the upgrade guarantee bonus. Seems odd.