Is it possible to trade a Gen 2 or 3 Pokemon to FR/LG before obtaining the national dex?

Question

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FireRed and LeafGreen seem to go out of their way to ensure the player can't get any gen 2 or 3 Pokemon before completing the game, like not allowing trades between RSE before completing a postgame mission, and even preventing Pokemon like Golbat and Chansey to evolve. But what would happen if an incomplete game of FRLG contacted a complete version and attemted to trade a Gen 2/3 Pokemon into the incomplete copy? Would this be the only way to get a non-Gen 1 Pokemon in FRLG without getting the national dex, or does the game do something to prevent this as well?

Answer 1

The player cannot trade Pokémon before getting a Pokédex from Professor Oak at Pallet Town. The player must have at least two Pokémon in the party in order to trade.
In a departure from the main series' tradition, additional limitations on trades were put in place, which cannot be lifted before completing the game at least once:
At the beginning of the game, trades are only possible with other copies of FireRed and LeafGreen. In addition, trades involving Eggs or Pokémon not in the Kanto Pokédex are blocked. Pokémon that evolve into a Generation II Pokémon by trading will stop evolving.
Obtaining the National Pokédex unblocks trades for Pokémon and Eggs outside of the Regional Pokédex.
Bringing the Ruby and Sapphire Key Items to complete Celio's Network Machine allows trades with Ruby, Sapphire, and Emerald versions.

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