In answer to your hypothesis, Banking Scot, alarms do sound! However, British Airways' Baggage Services' staff have the authority to "revalidate" bag tags or send "Rush" bags provided:

(a) The passenger who owns the bag is travelling on the aeroplane in question or

(b) The passengers has already flown on a previous flight and is waiting to be reunited with his/her baggage.

This is how airline staff, travelling on stand-by (subject to a seat becoming available) are able to "roll over" from flight to flight in the busy holiday season without constantly reclaiming their baggage each time they're told "Sorry, this flight's full!"

What is a definite No-No for CAA controlled airlines, since Lockerbie, is allowing baggage to travel before the passenger has travelled (except in the instance of baggage conveyed as cargo)! FAA controlled carriers regularly used to allow this, and Continental still do! Scary!