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Considering how many Pokémon got added and removed pre-Spaceworld, I don't think it's a stretch that during Red and Green development:
1. Multiple sprites for the same Pokémon existed in different slots, and the frontsprite and backsprite did not always match
2. Some of the scrapped Pokémon ended up in Spaceworld with some modifications, but most of these were scrapped too.
3. There were way more than 40 Pokémon added and removed during Red and Green's 6 years in development
4. Placeholders were used for some sprites, in fact the final MissingNumber sprite is glitched portions of the video RAM, but it likely had an actual "Placeholder" sprite in this point of development (think of the Pikachu or Igglybuff silhouette). Later games used a black circle with question mark.
Point 3 calls into question Helix Chamber's development narrative.
