This might be a bit of a noobie question, so I'll put it here...

I used to fly loads and got a lot of upgrades on overfull emirates flights. I understand how overselling works etc, but...

Do emirates ever upgrade from J to F if F is completely empty?

I'm flying to Haneda in a week and on the DXB-HND and HND-DXB leg J is about 70% full and F is 0%. Saver tickets still available etc.