If, as 'Nigel' posted, there were "30+" incidents of unlocked cowlings on Airbus, it seems that BA (and a significant number of the previous operators) failed remarkably to take the necessary steps to warn their staff.
As someone else had posted, it would seem that 'first flight' walk-rounds specifically SHOULD call for a thorough check of cowlings - or did the F/O fail to do what was called for?
How many events does it take?