The Commonwealth railways maintained two separate number series for brake vans.
Originally all the brake vans were given a freight vehicle coded that began with the letter "Z", and the next vacant number in a numeric list specially maintained for brake vans.
When passenger trains were introduced in 1917, the letter "H" was allocated to identify a passenger type brake vans and "Y" being used for freight vans. Four wheel van were also appended with the letter "S" and bogie brake vans the letter "B".
As a result of this change all brake vans were recoded and several former "Y" brake vans were converted to "H" codings becoming "HR" brake vans with sleeping accomodation. This resulted in gaps appearing in the brake van list as the
"HR" vehicles were assigned new road numbers from the standard gauge passenger vehicle numeric list.
It appears that subsequent to the initial purchase of brake vans during the construction phase, further brake vans were given classifications from the standard gauge passenger vehicles list, despite their being used on freight trains.