Yep.
That most likely would have been a HZ body bought by a dealer for a written off body on a HX.... possibly the parts van for a Holden Dealer that someone crashed and the body department decided to repair.... I'd love to know the real story.
As Innuendo and WB suggested, most people would have swapped tags, but a Holden dealer on their own workhorse wouldn't have even thought about it and once it was repaired and had served it's time would have been sold off in the used car department..... Paperwork was correct as it needed to be for rego and the rest is history.