Ah, ok, thanks - I was worried in case it meant there was a glitch or problem with the booking, but if it's just overbooking (and there's space for upgrades) then that's ok.

Sadly I suspect that on status-heavy routes such as these, there will be plenty Golds that get upgraded into J in order to free up a seat in W for me!

(Thanks for the ExpertFlyer results too!).