I was trying to use miles for an upgrade from Y to J recently on a flight from europe to DXB.
No luck with D class opening up despite EF alert setup, no luck with op up as Y was open and no luck at check-in as J checked in full.
I gave it one last try on board - J was still full, but F wasn't... so I did a double upgrade and flew the F suite home!
Too bad I ate my face off in the lounge in anticipation of the Y trip home.