Powerline appear to be under a misapprehension regarding the use of the "VR" lettering on these cars.
They appear to be producing models with "Second" lettering without the "VR" and models with "Economy" lettering with "VR".
Both of these are correct but they appear to be confused about the dates.
The cars entered service with "Second" class lettering on 15 April 1962 without "VR" lettering.
Photos on Weston Langford's site confirm this:
http://www.westonlangford.com/images/photo/101441/ shows the VAC on 6 April on trial
http://www.westonlangford.com/images/photo/101455/ shows much of the train near Bethungra
Enlarging these shots clearly show the lack of VR lettering and the name "Wimmera" on the buffet car.
I met the train in Sydney on 15 April and I clearly remember the name "Wimmera" on the buffet.
I believe the "VR" lettering appeared fairly quickly on the cars in service, certainly by 1963/64.
The change to "Economy" lettering occurred from January 1970, so the cars ran for up to eight years with "Second" and "VR"
This doesn't show up on the most popular VR websites simply because most of the photographs are post 1970.
In NSW, the word "Economy" was not applied if the car had only Economy seating, and at some time this change occurred to the VFS and VFX cars. So they had only the "VR" lettering and the car number.
In 1983, with the change to the title "V/Line" the VR lettering was deleted from the Spirit of Progress cars which continued to be painted blue and gold until the Sydney trains were merged as the "Melbourne and Sydney Expresses in 1987.
So VFS and VFX cars (and VFK cars) appeared in blue and gold with only the car (booking) number lettering above the top "gold" stripe between 1983 and 1987 (and some for some time on the merged trains post 1987). Not all cars had this final version before being painted Tangerine, of course. Powerline made this "no lettering" version in the 1990s.
Further information can be found in my articles on the "Spirit of Progress Cars" in:
AMRM #172 page 43 (Part 1)
AMRM #173 page 47 (Part 2)
AMRM #182 page 53 (Part 3)
and "The Victorian Railways S cars" covering the red and silver cars in AMRM 194 page 32.
I hope this clarifies the periods the vehicles ran with "VR" and "Second" and "Economy" lettering.