Backdating Qantas green tier status credits

Hi all, I am currently 70 status credits away from obtaining Qantas gold and my membership expires August 31st, I have 2 flights upcoming in August which will give me 40 credits (so will be 30 short), I was planning on getting the remaining ones from green tier.

I completed my 5th and final leaf (recycling) mid July, but it took 4 weeks to register in Qantas' system, and recently I have just found out that it takes another 21 days to select any reward - which would be September 3rd...

I rang qff this morning and they mentioned that it's possible to backdate this reward for the previous membership year. Has anyone had this experience and it worked? The person I rang seemed quite unsure themselves..

Any advice would be appreciated, thanks 🙏