A few observations...

1) Are you looking at each sector individually or both sectors as a trip? Emirates relies quite heavily on married segments so the availability can differ if searching segment by segment might show different availability.

2) I've noticed that Emirates will often still sell F seats even when J is overbooked to the point that the F cabin will already be full. They clearly take the view that the additional revenue from selling an F seat is greater than downgrading/offloadinga a J passenger. This is similar in J when Y is heavily overbooked

Sc0tty - if you share the exact date of your flights, I will see if I can get the exact load for you if it's T-48...