You'll be totally fine...I booked one reservation there for our early May trip at the 180 day mark for 5 people at the time I wanted, no problem. As time went on, I realized that we would have more people in our party, so on Christmas Day, I went on to see if there was a reservation for around the same date/time available for 8 people, and there was.
The rumor is that once every reservation is gone, they're gone - they won't show back up back on the Dining Reservation site if someone cancels a reservation - that's why you won't ever see a random reservation show back up in the system like you would at say, Cinderella's Royal Table or O'hana, etc. They do this to accommodate enough walk-ups and last-minute reservations at the resorts.
If for some very strange reason you do not get a reservation there when your window opens, you could probably just walk up and eat there when your trip comes around. Good luck!