What the cast member may have suggested is not something that is a guarantee. There is no guarantee of turning in a cash cruise ressie and making it into a
DVC points ressie..
DCL and DVC book from two separate inventories of availability. For example, when I booked my 2007 Med Cruise, there was only guaranty category 6 available, though you could see plenty of cat 6 rooms available for cash on the website.
So, you may go to turn in your cash ressie, and find you cannot rebook it on points as the DVC allotment is no longer available. You may be able to make the turnover, but find that you lose your selected stateroom and go to a guaranty category, or another different category according to what is available at that time, paying the points requirement for the category you end up with.
In short, what you see as availability in cash, is not the same availability for DVC points. There are selected staterooms, selected categories and selected dates at any given time that may or may not match what is available from DCL direct on cash. So beware of the "switch" option that the CM tried to offer you. It may or may not be an option for you down the road.