Exactly, if you randomly pick a date only for the sake of confirming/issuing the ticket, in hope of change the ticket to a desired dates later, you run the risk of getting stuck with the dates you didn't want(cancellation cost 3000 miles), or even getting stuck in your destination (you can not cancel return flight once you have flown the outbound flight, so you loose it, and you need to book a one way return flight for your desired date).