Yep, I had a Y BP on my original flight and when they were looking into the next available flights, they looked straight into F and told me one was all out but the later one still has F and booked me straight into that one. I didn't even try to ask but GA just offered it. There were other fellow bumpees in the F cabin too. The mileage credit remains the same though as nwa.com lists both Class Flown (F) and Class Purchased (K) and miles were based on purchased obviously. I remember someone mentioned this kind of booking called forced F.