Back to "standby" for a second...I was told by many GAs that their policy was to clear the upgrade list first, then clear the standby. I'm not sure if that's really the policy or it's just their way of being lazy...clearing all Y into F first, then clear standby in the remaining Y seats, vs clearing standby to Y first, then clear Y to F, and then go back to standby again to clear those into Y of those who got upgraded to F. Ultimately, it's up to the GA since there isn't a clear written policy.
However, I've also been told by GAs that if you standby, the computer automatically lists you as a standby for your current booking class. For example, if you have not clear'd upgrade on your original flight, you would be standing by for a coach bucket. However, if you have already clear'd, then you would be standing by for X or R for 3 cabin J @:-)
The people who are already on the upgrade list are also standing by for X. So, in this case, I wonder who actually has the priority?! An EXP "standing by" for X (essentially treating the EXP like a F passenger), or a Plat already on the upgrade list...