Oh, well spotted! *quickly checks my Pikachu collection despite you mentioning "It’s also exclusive to Ruby Sapphire AFAICT."* I’m glad Pikachu wasn’t in this set, though. 
But I’ll definitely remember it when I make new single Pokémon lists in the future.
Something similar is also going on with the Japanese Ultra Force (SM5+) set, although it’s a lot easier noticeable. The font is the same, but one is just black, and the other is black with white-outlined text.
Greetz,
Quuador