Now is a good time to explain that airlines do not have an unlimited amount of award space on any given flight. (themilesgenie.com)
Further, although modification of the type or amount of the award on the basis of a change in conditions is generally the rule, parties can agree not to modify. (info.legalzoom.com)
The good news is that there a good amount of award availability and there are an incredible number of Business class upgrades available. (travelingformiles.com)