I have always had a chance to select my seat when flying AS even when I book through my corporate TA. I've never been relocated to "the back- middle seats" either. (the only times my seat changes is when I am upgraded to FC, or I select a better seat myself online or on mobile app) Yet, I hear about this happening to people fairly often, (NOT everyday, or even as a routine, but enough that makes me ask about it) especially a family traveling together. How is that possible? Is it because they booked in one of the rows that does disappear when an aircraft is changed? (like just before the exit rows?) Is it because they wait to check in for the flight at the last-last-last minute? Or something else?