What do you call early? And is it a Monaro or a GTS or a GTS327? Remember there were pilots then online pilots before there were production vehicles and Dandenong didn't build any pilot HK coupes, they built a few online pilots: two Monaro (both 186, one aout and one manual) and a V8 auto GTS. They were all built around 23rd May 1968 (around right now 54 years ago). The really early pilots were Woodville and Elizabeth and built between 1st April and 30th April 1968. Volume Monaro production didn't start until much later on 20th June 1968 and GTS/GTS327 in the first week of July 1968.

That's not all that early in real terms. It is a reasonable way into volume production. Its VIN should be up around J126xxx-ish ballpark? So by that time you'd expect any anomalies with non steelwork stuff should have been sorted out. It probably still has the early pillars and the extra C-pillar badge access holes under the headlining though?

For example the one HK Surfers Paradise release GTS327 that was a Dandenong build was J124572 and it will have had a chassis number around HK20xxxM.

The strips are lower down near the sills
The boot not having the black paint and the chrome strip not having red in it
Is a mystery??

It didn’t have red in it when I bought the car 43 yrs ago ??

An advance Dealer Service letter dated June 26, 1969 discusses this very subject of fading of the baked on red colour of the HK boot lid trims.
GMH tells dealers to stop replacing faded trims with costly new trims that will also fade in a short period of time.

The recommended action is to repaint the faded red with an air dry enamel called 'Synflex' manufactured by Brolite Pty Ltd.
The enamel can be applied by brush or spray and must be thinned 80% colour to 20% Brolite Thinners No. 1000
The dealer claim allowance per vehicle for Labour & Materials was:
Kingswood & Monaro $2.25
Premier $3.00
Monaro GTS $4.50

On a car that's now 54 years of age, minor accident damage & repair early in life is a real possibility. That's probably the real reason for the lack of black paint on the boot lid.

You say you've owned the car now for 43 years !! I bought a cheap a Monaro (HK GTS 307) in 1979 which had previously lived near the coast & had that much rust that the previous owner couldn't get it re-registered, so we just stripped it down & drag raced it. These cars weren't worth much in that era.

Dr Terry