I guess you're correct but as the plate is riveted to a piece of the vehicle that's easily replaced it makes you wonder how many have been replaced/lost over the years.
I wonder if a Roadworthy tester would actually look for the compliance plate if the vehicle seemed 'standard' and they found the chassis number anyway.
Compliance Plates
Compliance Plates - Engraving Specialists - ID & Warranty Plates - Aluminium and Stainless steel plates - Laser colors
Back to the original question....maybe an advert in a local paper (around Emerald) would turn up someone who knows it's history. Did the seller have any details of where it came from, I'm sure it was from Melbourne and then went to Korong Vale.
Colin