Just a quick update: they have indeed confirmed the GVA-IST segment about 3 days before the flight. Of course that required me calling TK call center, and them sending internal note to the back office... very strange, complex and customer-unfriendly situation as you must call multiple times and have no assurance all will go fine until less than 3 days before the flight... I hope it is not a new standard, but just me ...or GVA departure...