But from a trading perspective, if you happened to have a Scyther on LG you could trade it to RSE. This isn't so inconceivable considering that you need to have unlocked the national dex in FR/LG to trade to RSE, whereas you can freely trade between FR and LG.
So you could have LG with the national dex, FR without the national dex, and an RSE game. You would have to trade the Scyther from FR to LG in order to trade it to RSE.
Life is just a series of problems that make you wish you were dead until you are!