I had the same thing earlier this year with Air Canada, arrived in LAX, waited ages for all the bags to be offloaded, nothing, walked into the baggage office and the lady immediately said "Are you Mr Airprox?". So she knew that my bag had not made it onto the flight I was on and was expecting me to appear, but AC had not said anything, no text, no email, no message from the gate agent meeting the flight, and no page from the lady to get me to come to the office, so 45 minutes completely wasted unnecessarily. So it's not just BA that is rubbish at these things unfortunately