I've just finished reading through this entire thread and am still not sure I am understanding mileage upgrades. I will shortly begin traveling to Europe and Africa several times a year for the USG, meaning (I believe) that my tickets will be Y-fare on U.S. airlines only, per the Fly America rules. In that case, as someone without any SWUs, am I able to upgrade using miles if I am flying DL codeshares in Y class operated by KLM or Air France? I will not be able to re-issue the tickets with AF or KL flight numbers.