My friend is able to lend me Red Dead Redemption. However it's the vanilla edition, so I'm going to end up buying the GOTY edition anyway. Here is a question now: If I were to play Red Dead Redemption, non-GOTY edition, have a save from it, and then buy the GOTY edition, will I be able to play on the save I made while playing the non-GOTY edition?
The DLC in the GOTY edition does not affect the main story mode as the DLC is all multiplayer based except for Undead Nightmare, which is stand-alone. You can purchase the GOTY edition after playing the vanilla version and you save will be okay.
I have contacted Rockstar support and they have confirmed that save files are interchangeable between the standard edition and the Game of the year edition.
This means that any save created with the vanilla edition will load up no problem when you get the GOTY edition.