The only time a WDW reservation number is needed is if you are trying to do the 180+10. As long as you are within 180 days of all the ADRs you want, you don't need the resort reservation number. If you are calling at 180 days out and want to make all of your reservations for that week, then yes you will need your WDW resort reservation number to prove that you are staying onsite and are eligible for the 180+10 benefit.