I posted a while back in the rugby World Cup thread that due to a change in plans, I was cancelling 2 x HND-LHR in J (I wanted to give people a heads-up as redemptions over this period are thin in the ground). Purely for my own interest, I checked before I cancelled - no availability; and I checked a short while after cancelling - the 2 seats were available again. So it definitely can happen; don’t know if the fact that these were the 2 guaranteed J seats released 1 year out made any difference.