Well there was some debate a couple of months back and I think we agreed we would not want to get flooded by other carrier's flyers taking away "our" upgrades (i.e. advance confirmation). However, Rudi and I came to a truce on this and decided it would be OK to give them out as last minute standby at the gate. Don't want the front cabin seats going empty if we have Star Gold fliers with a Star carrier's upgrade certificates! . . . but make sure you give your customers every opportunity first.
AC treats UA flyers the same way so I guess we are even. Some other Star carriers don't even get the luxury of upgrades!