Why is this a red flag? Every authentic Chanel bag should have its own unique serial number. When the same datecode appears in multiple bags across different countries, it usually means these bags are not authentic. This happens because manufacturers of fake bags often copy and reuse the same serial numbers many times. 

Please check the list below carefully. If your bag has one of these serial numbers, it may not be authentic. For your peace of mind, you might want to have your bag checked by a professional authentication service.