It seems that I unlock a character each time I win a gold cup that I didn't have before. For example, if I win the leaf cup in 150ccm for the first time, I get a new character, but if I win it in 150ccm again, I don't.
I only played 150ccm so far and got the gold cup everywhere. Now I guess I can't unlock any more characters in 150ccm. But can I unlock more characters by playing the lower difficulty, even though the cups and stars carry over to the lower ranks? Or is my only option to win 200ccm cups now? If yes, how can someone who started with 200ccm (and got all gold cups there) ever unlock every character?
It seems I did not state clear enough what I want to know, so I try again:
If I have won a gold cup in some difficulty for the first time (and unlocked a character by this), will I be able to unlock a new character by playing the same cup in an easier difficulty?
I have already tested that it is NOT possible to unlock a new character by playing the same difficulty again: I played the mushroom cup 3 times in 150ccm, every time with 60 points (=always first), but still only got ONE character unlocked.