Well, Sam, they (TDK) did make these, in my opinion. Why, I'm not sure. Possibly sales awards or something like that. They were not offered to the public (at least, I've never seen one when tapes were around) but I have seen several examples of these gold tapes, with various detail changes (TDK vs. JAPAN embossed in the shell). I think I asked the same thing about them over on TH, and subsequently did a bunch of research on them.
And I was even contemplating picking one up in the case, which was a blue velvet box with gold embossed TDK and logo on the inside of the box. The box was clearly "shelf worn", and appeared to be legitimate, rather than a "New" forgery like the "reel to reel" cassette tapes all over the place now.
In the end I did not buy one, as I figured the funds would be better spent on tapes I can actually use.