It depends upon what QF wish (through their systems) to advertise of flight/class availability to different fare sellers.

Have you done a 'dummy' booking and checked the seat map (via seat allocation)?

I would say the flight would be quite soon, as the x4 x7 type variances seem to appear in the last week or so. (i.e. It may have been J4 Y4 all until this week, when QF have decided to advertise more availability in WHY)