The baggage areas at LHR are an incredible sight ... literally mountains of lost bags piled up ... I say lost as the bags are just in a pyramid, clearly not being sorted or worked on for days at a time. Probably your bag is in such a pile. The detailed contents is irrelevant for compensation, the amount is based on the weight of the bag and is so much per kg, so I believe that IB is being honest with you in saying they are using the contents list to help to identify your suitcase. External tags do fall off -- this is why I also have 3 tags inside my suitcase, in various places (shoe pocket, cosmetics pocket).