33tony – After a Development Consent (DA), and I think even after a Certificate of Occupancy has been issued, the original Applicant (e.g. the Developer) can apply to Council for approval to modify any past Consent under the provisions of S.96 of the NSW Environmental Planning and Assessment Act (1979).
Requested modifications have to leave the development “substantially the same” as in the original DA, and even though that criteria is subjective the changes you mention in your post would be permissible under S.96(2).
So check that possibility with Council in the first instance, but if there have been no S.96 Modifications approved, and the Construction Certificate which was likely provided by a Private Certifier engaged by the Applicant is inconsistent with what’s on-site, then it’s Council’s responsibility to ensure that the Owners Corporation (O/C) complies; assuming it’s the one who has left matters in a inconsistent state.
I’d recommend an approach to your local Councillor / Alderperson to stir Council’s Officers along, followed by a letter to the NSW Department of Planning, and if all else fails an Application to the NSW Land & Environment Court.