There's a potential ambiguity, I think, between "100th" and "uniquely pertaining to 100". For example, if we are orded by our ages, then I am pe li 35, but I am not 35th. So {me li ci mu me'u moi} is potentially ambiguous.
But {moi} has an x2 and x3 to disambiguate. You can specify in which set and by what rules you're ordering.