I can recall a situation or two where despite a handful of empty seats all the way up to departure, it looked like the award inventory never opened up at all.

It would be best to get on the waitlist, sometimes they'll just clear directly from that instead of opening inventory to the public.

Of course you can only do so if you've redeemed OnePass miles for the reward (either on the same flight in coach or on a different flight in either coach or business).