How can compartment bay loading informating be derived from the IATA load message (LDM)?
Paranee,
There is no such detail in the LDM, it is just a WEIGHT value. There maybe specifics for certain SL/DG (review AHM again for those) as some SL/DG are required to show location and some location and weight - explained in AHM.

BUT - LDM is just an overview, not very specific as it does not need to be. For a through flight A>B>C, where A is OFFLINE to your system, if you have received teletype LDM for processing and you are doing the sector B>C then any load B>C is just shown (know by the system) as TRA (transit) load - nothing more. No more detail.

However for unitized aircraft, the CPM complements the LDM to show the detail required by bay as opposed to HOLD and/or COMPARTMENT.