Appreciate the education today. Indeed, I discovered that AA cancelled the duplicate travel (the segment I intended to fly). Just off the phone to fix things, ponying up $203.50 for the change fee.
Live and learn. I have 400k lifetime with US. Know I've done something similar a couple times in the past (actually, once was last year under wife's itin - was able to salvage credit toward a later, more expensive itin, net chg fee).
Clearly AA is absolutely rigid by comparison. I get rationale, though. Thanks again!