Hello Nigel
You probaly have already seen these sites:
http://www.defence.gov.au/cfo/tax/supps/iraq/default.htm
http://www.defence.gov.au/cfo/tax/03/default.htm
Defence has their own tax site on the internal web, I will have a look tomorrow at work and let you know if they have anything on s23AD vs 23AG.
They also have hotline.
"Defence Hotline
The DTMO provides an email and hotline service to assist ADF members with queries relating specifically to the Iraq Supplement. Please send your inquiries to the following email address:
[email protected]. If you do not have access to an email facility, you can contact DTMO during business hours (AEST) on 1800 806 053. "
regards