I had registered that it was a 738 (I'm not a Spotter, promise!) but the Demo talk said "Under Your Seat". Since I was not aware of the NG storage option (which sounds very sensible) then I think that, had the crew advised that, it would have stuck in my mind. Also, when I checked under my seat there was the usual 'sling' pocket with the front closure tab hanging down, so it was easy to verify that the pocket was empty. If the a/c was equipped with O2 jacket storage, would they still have provided the pocket?
Now I have to write to that FRiggin' airline ...