I came across this interesting piece of information which totally explains why when travelling West to California my baggage went in the opposite direction, East to Oz!

The following article was taken from the July edition of the IATA newsletter:

What’s in a message?
Did you know that behind every bag there is a message that tells the baggage system what to do with the bag? This message is crucial for the delivery of baggage. One of the common reasons for baggage mishandling is the lack of a BTM (baggage transfer message) agreement between airlines. The BTM is used as a fallback between airlines when an EDIFACT transaction fails.

The BTM is received by the next airline to handle the bag. If the airline cannot process BTMs or there is no BTM agreement, the bag will not have the much needed message and will be sent to the default system output, perhaps missing its connecting flight.

BTM agreements are simple to make, and all modern host systems should be able to handle BTMs. These and other solutions are part of the Baggage Improvement Programme solutions. Toolkit.