The 4 eligible flights are required if you want to gain Silver/Gold/Platinum Status. What class are you booked BNE-ABZ?
I booked through BA as WT+
The tickets are:
BNE-SYD on QF ticketed BA Y
SYD-SIN on BA ticketed BA T
SIN-LHR on BA ticketed BA T
LHR-ABZ on BA ticketed BA J (although I think it's an economy only flight, so go figure)
On return it's ticketed as:
ABZ-LHR on BA ticketed BA J
LHR-SYD on BA ticketed BA T
SYD-BNE on QF ticketed BA Y
It's not a big deal anyway. Even if BA ticketed flights alone were enough to qualify, it would only apply for 20 days after I got back anyway.