LB, your question is rhetorical. “how would APTA know? the answer is the same as that of the local flying school. APTA relies on trust - exactly the same way as the local school.
Short of a full blown telemetry system (eg ACARS) all operators rely on their staff to tell the truth in a timely manner and follow the procedures. If they can’t be trusted then there is no way in hell that ANY system can generate an accurate outcome.
‘’By definition, APTA surveillance can only ensure by audit that (a) Members know how to use the systems. and (b) Members are trustworthy.
CASA is entitled to ask APTA about matter (a) - which involves training. Item (b) is satisfied by the application of the fit and proper person test.
To put that another way; a mate was until recently a training and checking Captain on a very, very major international airline. The assessment of a pilot by him is still a matter of trustworthiness- and he has at least one story about this subject.
It is not possible to guarantee that humans will always behave and CASA has no business requiring APTA to do the impossible.