Core icon usage points are only incurred when an icon is used for the first time within a set billing period. If the same icon is used again within the same billing period no additional points will be counted.
This means once you have used an icon you are free to use it as many times as you want within that billing period.
If this icon is used again in a future billing period, it will be charged a usage point accordingly.
Please note: You are not charged usage points for using your own private icons.