>>35750623Anon. It was either done from scratch, or it wasn't.
If it wasn't done from scratch, then it needs something to be based on. A base. If this was true, you'd see the code from the base game. A Red romhack, for instance, would show code from Pokémon Red.
But this isn't the case. The code is too different from any other games, both 1st and 2nd gens. Therefore, it was done from scratch.
Now, one question remains. Why can Pokémon Stadium recognize these games? If it could've only recognized RBYGSC then these games wouldn't have been recognized. But that isn't the case, clearly. Stadium 2 can recognize the beta GS games. Why though? The simplest possible explanation (the one that allows us to make as few assumptions as possible) is that these games were meant to be connected there, therefore they're legit. The other explanation is that this is a very elaborate ruse, but this forces us to question ourselves why this is even a thing. It leaves too many questions open and explains nothing.
Therefore it's likely that these games are legit. I don't see a reason why we should believe they're not.