you may want to also check the availability for pay ticket for your routing and then check the award seat availability BY EACH SEGMENT of the routings shown on the pay ticket, using One-Way button.

many times there are award seats available by segment, but it would not show up if you ask for award availability as a round trip. My guess is if the routing is not a most direct route (or not too much out of the way), it would not show as available for award booking. Also a layover longer than 4 hours wont show either, unless if you are desperate, you use the layover as a stopover. (Personally I would not waste my stopover that way though).