Trainage Pitts

We are wanting to covert our back garage into a granny flat. Building and trainage was approved under Baulkham Hill Council at that time. Now under Parramatta Council they are stating that we are unable to do this conversion due to the change of ruling to Trainage pitts.
When contacted Baulkham Hill Council they informed that they do not keep records that far back. Hence we can't prove that all the work was approved. Can anyone share some light to this matter or how to tackle this situation to get approval to satisfy Parramatta Council.