I've just had my upgrade approved for a Perth - Melbourne flight a few days out.
I looked yesterday and there were a lot of spare business seats and now post upgrade there's about 6.
As mentioned, they would go through and upgrade any wait lists, bids etc. Which ever why they work it out.
I have also started to notice on "Coast to Coast" flights they don't seem too keen on having more than 1 business reward available in advance ... I think this has a lot to do with the a330's heading to Asia and B737 business class changes.
Though if this is the case, closer to takeoff they will release more J reward seats.