BA only guarentee to release 4 economy and 2 club seats on every flight. There is no commitement from them to release WTP and F. Nor is there a commitment to release any more seats once the initial allocation has been taken up though of course they often do depending on the route and time of year.
Some routes are very popular and people make the effort to be ready to book bang on T-355 days when seats are first released even if that is in the small hours of the night. Ref the many posts asking what time the seats are released.