@WurstEver I've been working on this for a while, I didn't realise until I acquired two and noticed the slightly different print density on them, both totally original and not the later (from 1980's) service replacements. They are so rare and difficult to distinguish between original and service replacement that there is little photographic evidence to go on.
The example fitted to my 2016 image I believe is iteration 2, the iteration 1 had exactly the same format but the printing was more accurate and thinner.
My research continues and as and when I find something new I will report back
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