Someone paged me?

Make sure you have copies of your updated reservation showing you in F class, even without a seat. In the event you are downgraded back to coach, you should insist (escalating to a supervisor as needed) in the compensation listed in SHARES at GG OVS DOWNGRADE (and be prepared to write to 1kvoice if the airport refuses to issue your compensation, capturing staff names for your complaint letter) - the $300 or so dollars you will collect for the now involuntary downgrade should cover the risk of a crappy seat in Y should this turn out badly.

Without those copies, you'll have no proof that you were ever upgraded to F - so include copies of the pda site upgrade list, the reservation and any receipt you can generate that shows your updated cabin class.