There is really no way to predict upgrades. We've had them on 2 of our 9 cruises. September is not a crowded cruise month, making it more possible to have upgrades then.
It really doesn't seem to be based on when you made ressies or anything sensible. We've booked 18 months out and not gotten one. I've seen people book and get an upgrade within 8 hours! For us, one was at the port when we checked in, on another the TA called and said one had been offered a couple weeks before sailing.
The key is to book a cabin where you will be happy, then consider an upgrade as a gift if it comes your way.