This one blows my mind. That background image, of the Pyramid of Power, absolutely has to be true official art they simply never reproduced anywhere else. Why do I think this?
In several issues of Famimaga, an official Nintendo Magazine in Japan, they started off the Link to the Past feature each month with one of the other official images. Like Link smiling at the maiden in the crystal. This is the only image from that set that is not in the booklet for the game. And the quality is just as good as the others and the style is so similar to the other animation-style backgrounds. I really have no doubt that this is official but simply stayed on the cutting room floor until someone grabbed it for a filler image for their magazine. It's not like something this high quality was made just for the magazine (and just to be covered up by that other random art.)
Anyway, I'm devastated that we will probably never get to see the full image of this. For all the guides, magazines, and merch I have seen over the years: this is the only place this appears. As far as I know at least. However, if you see it somewhere else, please write me right away and let me know.
Find the 2400dpi scan here. It is specifically from the 1992 no. 03 issue of Family Computer Magazine
Here are some photos twitter user, Number 20, took to show us (Thank you so much for your help!)