I flew DFW-PHX yestarday, no seat assigned and the seat map had been full for days. I'm a plat, so could see the elite seats were taken too, and 757, so no bulkhead reserved for ADA. And the flight showed F0 A0 Y1, so no one was getting upgraded out of coach.

Anyway, yesterday morning, about 3.5 hours before the flight, I logged in and checked again, and about 10 seats were suddenly available, mostly middles, but a few aisle/window, and one exit row aisle

I have 5 more DFW-PFX legs booked over the next few weeks, and 4 have either no seats open or just middles near the back. I'd rather have no assignment than a bad one. I figure gate agents may be too busy to accomodate seat change requests, but as a plat, the odds of my getting IDB is low, so my odds of a decent seat are better if I have none to begin with.