Thanks!!

By putting all the sprites on one horizontal line in the top “border”, the demo also proves it’s not using any of the standard tricks to fake extra sprites. The only thing that the C64 will draw up there are real sprites (not character/bitmap graphics), and you can’t multiplex sprites in the same horizontal line of pixels.

Not really the point: that is a tongue-in-cheeck trick, as we know how to solve that problem - but it takes using different stripes of the screen, whereas in the demo they are before 2:00 all put in the same stripe...

At that point we go "Ah."

(It's very normal in illusionism: the practitioner states something that puts you in the relaxed mood of participation to a game you know - then actually surprises you.)