Thank you all for the responses. I'm glad to report that my bag was delivered on day 14. Similar to Phil the Flyer, I was categorically told by QR reps multiple times in ATL and DOH that my bag was loaded on the same flight as the rest, and was lost in ATL. I learnt that Qatar Airways baggage handling in ATL was contracted to Menzies Aviation and I spoke to their employees as well. If anyone's bag goes missing at your destination airport, find out the local baggage handler and talk to them as well. File a report at the airport's lost & found office as well. In ATL, passengers who misidentify and take someone else's bags are directed to return them to the general Lost & Found of ATL airport.