I was asked when checking in for a 9k flight last year Has the bag been in your posession at all times, to which I rather truthfully said No. The agent looking slightly alarmed then said alright could anyone have interfered with the bag at all, to which I truthfully replied yes - I've just stepped off a BA flight from LHR and the bag has been out of my posession since I Fast Bag Dropped at LHR.
Visibly relieved the check in agent said you do not need to worry about it if it has been in the posession of another airline. So there you go.