The QF A330 fleet has, I believe, numerous S/Os who were nominally brought in on a Friday for a "start date" and then joined additional A380/747 recruits on the Monday for the remainder of the induction process. They are senior to the Monday joiners forever, and the step was supposedly taken to get the "right candidate" on the right fleets without them being perpetually on the bottom of the seniority list after they lost the "day one lottery".
That's the rumour anyway...