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American Airlines and US Airways continue to operate as separate carriers (though both are part of the same parent company through the merger), and will continue to do so for some time.
As this question relates to the American Airlines operation, it is being moved to the pre-merger American Airlines forum.
/Moderator
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Yield / Revenue Management algorithms that automatically release (or not) 'SAAver seats are based on historical loads as well as predictive analytics, modified by actual sales. A seat may never become available, cancelled seats may not be returned to 'SAAver inventory, or may be released at any time. Using a service like ExpertFlyer to alert one to a seat release might be a decent investment.
N.B. You may wish to read the following thread (and of course, the FAQ "sticky" thread).:
MileSAAver / SAAver Award Availability - Assistance & Discussion (consolidated)