No one will ever come out and say this because officially they are giving preference to internal applicants but...
Obviously they are coordinating their interview dates with the operational requirements with each AOC. I know this happened to cadets within QLINK who were all told it was "merit based". They couldn't afford to lose 25 captains in QLINK in one hit even if they were the 25 best guys and girls. They ran courses with a mix of FO's and captains to make in manageable for QLINK.
It makes perfect sense and is a smart way to do it. It's not fair on the individual who may be held back because they are a training captain or because they are under crewed in that airline. I'm sure merit based is then applied once they have decided they can afford to lose you from your said position.
My opinion only and based solely on observation of this thread and talking with people.
Ps, holding back 777/787 rated guys for the introduction of 787 also makes a lot of sense too.