Fortunately/unfortunately there is no central control over rates or inventory. Each property loads whatever they please whenever they please. Extended future rates may be low and then go up as the date gets closer and then drop a few days before if bookings look light. It's just like booking air fares, they can change on a daily basis, at some point you gotta pull the trigger and hope for the best. The nice thing about hotel bookings, unless designated as advance purchase and no changes, you can still look for better rates and usually get it (just watch room types).