I've noticed that, with Australian-made vehicles, Holden is the only one which seems to have the chassis designation displayed as part of the thumbnail information on each movie's page.

For instance, a 1968 HK Holden Monaro will have "1968 Holden Monaro [HK]" under the thumbnail, where other vehicles won't. For the corresponding model year, a 1968 Chrysler VE Valiant will have "1968 Chrysler Valiant" rather than "1968 Chrysler Valiant [VE]", and a 1968 Ford XT Falcon will list "1968 Ford Falcon" rather than "1968 Ford Falcon [XT]"

Of course, the chassis info is displayed on the vehicle pages - just wondering why it's displayed for Holden on the movie pages, and not for others...

There are a few makes in such cases
The following are concerned:

mercedes-benz
maybach
brabus
porsche
faw-volkswagen
shanghai-volkswagen
volkswagen
alpina
bmw
rover
lotus
jaguar
hsv
holden
statesman
vaz
lada
vaz lada

these are makes where models are first sorted by chassis, the by model name
also, chassis is displayed because more important than for other makes

it was originally made for bmw, mercedes and holden
then used for others where it fitted well too

problem with chrysler is that it would have an interest only for austalian models

that will be handled much better in the next version of the site