It is very strange.
Victoria's indexes show the district of the death registration right into the 1980's.
Plus MMS if known and other details, while NSW has a cut-off at end 1973 for revealing the district and slips into code at that point.
Admin at NSW BMD has in past years been reluctant with the communication side of things and their disinclination to reveal the meaning of the codes is typical and unhelpful .
I have even seen this -
JOHNSON William Edward
Reg 17417/1976
DIED DARLINGHURST
Mother- 066District- 001
Ironically, you cannot use the code in any of the boxes on the search. For instance where there the box for district at the bottom of the search page, putting a code in there does not work

Bewildering really.!
Sue
ADDING
I do note that in the instance of the PDF being "readily available", the district is stated