I'd wondered about this one after seeing it in your book, having never seen one before either. Discolouration did cross my mind, as the remainder of the dial has bubbled in places but the beige colour looks too uniform for that and the paint on the indices and numerals seems completely unaffected too. I note the one in Chuck's article uses the other version of the Tachy index ring too so it looks like there's at least one more out there. I hadn't seen the lack of ridges on the indices before that big close-up but can see it in the book too now I look properly :)

So it's great to hear that Gerd-Rüdiger Lang was able to confirm that this was original.

I wonder why Heuer didn't proceed with production of these after the trial - for my sensibilities, at least, it's a particularly handsome combination and I would have thought customers in the 70s would have thought the same. Ah well, makes it all the more desirable now! Another one to add to the want list...