To make sure I understand this "one year heads up":
I just re-qualified Gold until November of 2026. I can not re-qualify one more time under the old rules, correct? The next re-qualification would need to be under the new rules (12 flights)?
Everyone gets to requalify one more time under the old rules.
It all starts tomorrow. All those whose year ends on 5 November will requalify tomorrow - for the final time - under the "old" rules.
This procedure continues until the very very last people to requalify under the old rules will do so on 4 November 2026, exactly a year from today.
(PS: don't confuse the act of having already banked the required number of sectors and Tier Miles with the act of actually retaining status;
you requalify on your anniversary date, NOT on the date you surpass your retention target. If your M+B account tells you that you have already done enough to retain your status, you must still wait until your current membership year ends before you actually "retain" the status.)