The ACT website says you get to choose the scores you want to send to any college, while some college websites say they require your entire history of tests. How would the colleges know whether or not you sent them the whole list if you don’t send them the whole list?
ACT scores are reported one test date at a time (you pay the fee for each test date), so the colleges don’t know if they’re getting the whole list. Of course, you can also delete ACT scores so that they’re no longer reportable in the records.