Are the platforms separate instances of the same platform object? if so, give them an instance variable or boolean that toggles when the event first triggers/score is given. Then add a second condition into the landed event that checks that the variable/bool isn't set.
So something like :
Event - platform on landed
Condition - platform (family) > compare Y > platforms 'greater than' player.Y
Condition - hasScored(inverted) --------- give score, toggle hasScored true