Originally Posted by
3Cforme
Not every seat on the plane is available for pre-assignment. (And recall that overbooked conditions mean more people than seats, so even if all seats could be assigned some people would be denied.) Delta may hold back something like 15 seats on an A319 for assignment at the gate. Check again for possible openings (as elites get upgraded from 5 days down to 3 hours in advance of scheduled departure) but don't worry about it too much.
On the 319, there are 3 rows in economy (the first row, the row in front of the exit, and the last row) that are held for assignment at the airport even though they show up in the seat map as occupied, so even though the seat map looks full, there are probably 18 seats still to be assigned.
It would seem like a good idea (and probably save Delta a lot of phone calls) for them to change the symbol on the seat map to indicate "airport assignment only" to calm fears of passengers who think there are no seats left and they are not going to get on the plane (I hear people say this frequently, and then explain to them how it actually works).
Checking for available seats at the upgrade windows is a good strategy. If only middle seats are available, the airport-assigned rows create another strategy... if you can't pre-select an aisle or window and would like to minimize chances of getting in a middle seat, don't choose a seat at all. Try to let the assignment happen at the airport, where you at least have a chance at getting an aisle or window in one of the held rows. If only middles are available and you take one, that will be your seat and you have no chance of a better one unless you are able to snag something with frequent checking of the seat map.