UC seats?

We are booked to fly to GND in October on a VS flight as part of a VH holiday. We're booked PE out and UC back.
Today I noticed the price had dropped considerably so tried to cancel and rebook flying UC both ways at slightly less than we were originally paying. Hope that makes sense?
I got as far as paying my new deposit but the system wouldn't generate an authorisation - then after a long wait I was told the VH site was showing Z seats as available when in fact only Js were - so my cheaper holiday would in fact cost £3,000 more per person! Luckily I hadn't cancelled my original booking - though I have a fight to get my new deposit back I fear.
Anyway, my question is, Expertflyer is showing 9 Js - are any Zs likely to become available to VH between now and October so I can upgrade?
Today I noticed the price had dropped considerably so tried to cancel and rebook flying UC both ways at slightly less than we were originally paying. Hope that makes sense?
I got as far as paying my new deposit but the system wouldn't generate an authorisation - then after a long wait I was told the VH site was showing Z seats as available when in fact only Js were - so my cheaper holiday would in fact cost £3,000 more per person! Luckily I hadn't cancelled my original booking - though I have a fight to get my new deposit back I fear.
Anyway, my question is, Expertflyer is showing 9 Js - are any Zs likely to become available to VH between now and October so I can upgrade?