It would seem to me that the sensible way to cope with the accreditation
of 'foreign' railways in NSW would be to do what the road transport
authorities have done ie establish an 'exchange' accreditation with
other States. You can register a car and get a drivers licence in any
State, and by virtue of this you can legally drive that car in all other
States - even though the criteria differ from State to State.
Keep it simple for goodness sake, and it shouldn't be necessary to turn
any blind eyes or to make assumptions such that 'the land between the
track fence boundaries on the Deniliquin line is in Victoria' which
would not stand up in court if ever challenged.