Had the same problem in August. No F inventory with the FC award.

Not sure what bucket the premium award pulls from, but the CP desk suggested using it because we (Mrs L4P and I) could and were upgraded immediately. Of course being a CP my upgrades are unlimited. According to the CP desk, all there had to be was open FC seats

I am fairly sure that seats have to be available in coach in order to book and then upgrade the award. If I'm wrong, am sure it will not be long until someone points it out.

BTW, I continue to get comments weekly on the luggage tags. Thanks for the effort in getting them made.