Reserving Marriott Maui Ocean Club, Napili

I was in escrow to purchase an even-year 2-bedroom oceanfront Napili tower. There was a contingency on the seller being able to reserve the unit for me for Aug 11 next year. They were unable to do so, indicating that it was already full-booked. So, my question is, does anyone have experience with booking these rooms at the Napili Tower? How hard is it to get a place one-year in advance? Is this a common problem at this location, being unable to book your owned-timeshare a year in advance? What is the booking window for Marriott?