Okay, I downloaded a save file off the internet for a game. I had assumed that it was as simple as renaming the save file (after converting it to the right format) so it matched the name of my game (i.e. if the game is "1234 - Game A.nds" the save should be "1234 - Game A.0") and copying it to the same folder but that doesn't work - it doesn't recognize the existence of a save file and acts as if I have never played the game before. I tried this with multiple save files so I know that it's not corrupted.