<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Old Gold:
The catch here is that you have to be confirmed in the Y seat before the upgrade can be processed.</font>
Golds and platinums should always be able to confirm a Y seat >24 hours before departure.
In a service interruption, you can be confirmed directly into A, even if you're not traveling on a Y fare.