Reading this thread spurred me into action for myself. I'm taking the family back to The World in November, and last month or so I got a notification that my flight numbers changed. I thought I'd better call DME and update our info, just to be safe.
The CM couldn't find me by name in his system. He asked when I was traveling, and then said that his particular system only has data for the next month or so and not beyond that. He advised me to call back in September or October, but he DID advise me to update my info at that time even though it's only a change in flight numbers and not times.