I don't have experience of the OP's precise problem, but I noticed in my partner's account that QF seem to have got quite sophisticated with this.
Year end 31 October.
Outbound flight on 26 October credited on 28 October.
On 31 October, SCs reset to zero.
Return flight on 29 October credited on 1 November - with a note saying these SCs do not count for the current year.
So if "prior year" flights are now comprehensively trapped both for automatic and manual posting, I expect that QF FF would have no problems in adjusting the OP's tier level accordingly.