I recently played some Super Mario, and was saving to slot 0. I went back into Super Mario a few days later (which brought me back to the first World) and instead of pressing load saved game (Select/ L2), I pressed Save (select/ R2).
Has this overridden all of my previous game (I got to the second world)… Or can I retrieve this file some how?
If a saved slot has been “saved” again, there is no way to return to the previous save. I normally choose a hard-to-get slot such as 7 (not 8) for moments where “if I loose this, I’ll likely cry”. And save slot 2 (not 1) for quick-saves.
Having two saves helps with worst case scenarios.
You could clone an image of your uSD card if you wanted to backup everything (all games, all save points). That’s a bit more involved (but worth it once every now and then!)