Just to pick a nit, 'instant' in your case means once you had your booking confirmed, you were able to go back online and request the upgrade; as R was available, you were able to confirm the upgrade and choose a seat in J cabin. The word 'instant' that seems to confuse folks is that it implies no further action upon booking Latitude. Which is not the case. Going from 'available for upgrade' to 'upgraded' requires the self directed action.