Originally Posted by BobFF68

I have no experience about ATL-IST, anyway relying on EF seat map does not give any useful information, on TK traditionally many of seats are taken during OLCI even in J, I would rely more on flight availability. As example during my last CGK-IST-MXP return availability was already C0/J0 on 3 legs above 4, but 6 days before the trip the seat map was still showing different free seats, at the end 3 legs J cabin was full and one just having a single free seat. Maybe you will be lucky but relying on a last minute upgrade in this busy period of the year may revert into accepting the last seats that has been left in Y.