I once heard that when you request a credit online because a fare has dropped, your confirmed upgrades (SWU for example) are lost and you have to re-request them. I have no idea if this is true, however, in the past it's made me unwilling to risk losing a "bird in hand" upgrade even when I can see that the ticket price has dropped below what I paid.

In the next few weeks I will likely be buying two expensive economy tickets to SGN for my husband and myself at around $1600-1800 each (travel Dec/Jan) and using SWUs to upgrade, in order to travel on the same flight that I can find two award seats for my daughters. I'm pretty sure that the fare to SGN will come down between now and Dec and it would be nice to know that I could get a refund for the fare difference without risking our upgrades. What's the true story here? thanks for your advice.