Generally, British Airways (BA) starts a new tier point calculation period after the collection of year.(My current Tier Point collection year ends: 8 March 2025)
I am currently at Blue status in BA, and I want to start accumulating tier points. However, I have three long-haul flights from Europe to Asia with Cathay scheduled before March 2025. .
If I credit these flights to my BA membership now, the tier points will reset to zero, and it would seem like a waste.

My idea is to book these flights without adding my BA membership number in these Cathay flights. After April 1st, I would retroactively claim the tier points for these flights.

My question is: If I claim these tier points after April 1st, will they count toward the new tier calculation period, or will they still be credited to the current period (before March 8th)?
What steps can I take to ensure these tier points count toward the new period?

thank you for your help