The situation is this.......

It is my daughter's 21st birthday this year and she has always wanted to go to Tokyo. I had enough miles to book economy flights and also had two PE upgrade vouchers. There are however three of us but then a sale came along so my miles went further and i could now manage three return flights. These are duly booked out on 21/6 returning 29/6. I also had two PE upgrades so rang VA to see what I could do with those. I was told there was availablity on the outbound leg but there were no PE reward seats released for the return leg. I was advised to book the PE outbound in case they disappeared and tokeep calling back for inbound availability. As advised I did this and having been ringing every week or so since September last year only to be told there are none. The thing is that if I try to book a one way PE reward flight using miles only it says there is availability or at least it tells me to choose a flight. Can anyone shed any light on this as to if/when reward flights will become available or could it be that I am being told there are no flights available when in fact there are? Any help or advice would be appreciated