Flight bonus points tier points (plus Avios for the flight based on distance flown) will post for each flight a few days after the specific flight is taken and be referenced back to the flight date. So with a booking either side of year end the outbound flight bonus will post in the old year with the return flight bonus in the new year.

The BAH tier points (based on your spend) will post after the holiday is completed (usually 7 to 14 days after completion of the holiday) and aren't referenced to any date of travel so will post into the new tier point year in full.