I have purchased a round-trip flight (four segments) from Travelocity, as United flights, all operated by Lufthansa. I'm crediting the flights to Aegean. I'd like to choose a seat. The Lufthansa web site denies any knowledge of "online check-in code" provided by Travelocity (which appears to my untrained eyes to be a six character record locator). This is about 30 minutes after completing the purchase. Do I need to wait for the ticket to appear in Lufthansa's system, or do I simply have the wrong locator? I don't have status with any of the carriers involved; I don't even have an account with Lufthansa. Am I entitled to select an exit row seat? What is my best chance of getting one -- on-line seat selection, calling, or waiting until I'm at the gate?