Mach,
As stated, the SCPL had "permanently valid" written on it.
My view is CASA did not have the authority to issue a "deadline" when they knew or ought to have known that overseas pilots would be excluded. Its a form of retaliation for having left Australia to work overseas.
It's also a form of intimidation of what CASA can do to you if you go overseas.
Intimidation and retaliation are examples of bad faith conduct.
The other rationalizations are irrelevant.