Just remember, even if there is an F cabin on AF, NW WP members do NOT have access to the F seats. There isn't even a fare code to book F seats into, according to several WP reps on the elite line. MH, however, (for some very strange reason) is available, and usually costs the same miles--you just have to know to ask for them!
They told me we can't book F on AF because NW doesn't have a comparable F cabin for FB pax, but of course that doesn't explain why DL, CO, and KL members might be able to book F on AF.......