Couple interesting datapoints. Did a sort of last minute trip to AVL for a client engagement - booked 7 days before the trip began.
IAD-CLT did not clear at my 72 hour window but the return CLT-IAD (return the next day) cleared pretty much at 72 hours. The IAD-CLT segment cleared about 30 hours out.
Interestingly, owing to a mechanical oopsie on my AVL-CLT flight, AA protected me on a later CLT-IAD flight. I wound up not needing the protection, but apparently there was only 1 seat open on the protection flight and I cleared the upgrade list after being added to it by the agent at AVL. Cleared the list about 2.5 hours prior to departure.