Yes, you have to copy the content of the entire save folder. Without the .global the game doesn't know what saves are in which save slot.
Not if you still have the save files.
You can move them out of the folder. Create new saves in those save slots, and then overwrite them with your old saves. The preview in the loading screen will be wrong until you save and load again, but the progress will be that of your old saves. Just make sure not to overwrite your old saves.