Thanks to all for helpful input. Communication with United complicated by limited English-speaking phone agents who seemed to be reading scripted responses that did not address my questions. Repeated call-backs finally yielded native English speaker who did comprehend my questions & at least provided file reference number (but not Delta tracking number). Online tracing results indicate "arrived at airport" (didn't specify WHICH airport) one day late and "delivered" (but didn't specify delivered WHERE) two days late .. yet our hotel bell desk claims no sign of bag yet. Hotel clerk has left msg with Delta baggage agent at AUA airport asking for update.