Originally Posted by JonNYC

The only way they'll extend the hold is if the inventory is available (outside of what you're holding)-- so, assuming not, you won't be able to extend.

The other issue is problematic as if the other PNR was cancelled and no longer exists, they may very well see it as a new, within-21 days, booking. Normally, of course, one would be holding the award, PNR creation date being what it is, and simply have them change it to the higher class. Hopefully in your case someone cam listen/see the history and get it waived.