I don’t understand why ABC TV stations need to have a callsign that starts with “AB”, really. They could have just had “A”. So, using Queensland as an example, the Brisbane station is ABQ, but the regionals could be ACQ, ADQ, AFQ etc etc. and use them up before moving to four letters.
Then again, why do TV callsigns only have 3 letters, one of which is dictated by the licence area. Four letters would have been better and then they’d all have been uniform.