@lizzie86 From my understanding, a COGS is critical because it implies that during your nursing career you do not and/or did not have any impediment to be registered as a nurse in Australia.
Do you have written communication from your employer regarding this or just verbal? This is just an opinion and not based on experience.
Considering your situation, you can execute a notarized Statutory Declaration explaining the matter and attach Professional Reference(s) from a nursing supervisor, nursing director, or even a colleague. State something like:
you are employed as a _________ nurse with _________________ hospital from _________ to present;
COGS are provided by MOH for MOH run hospital and by the hospital itself if private
they do not issue COGS unless employee has resigned and/or finished their contract.
It would be helpful if in the professional reference(s), the referee can provide official communication channels like official hospital email (not yahoo or gmail) to facilitate should AHPRA deem it necessary to verify.