This forum has "Professional Pilots" in it's name and one would expect that the basics of location indicators etc would be taught at some stage during the learning curve. Sadly like many other 'little' things that does not appear to be the case these days. As for ASSY, that was correct once upon a time, we are just showing our age!! The second letter back then referred to the FIR as in AMML and APPH etc. Those FIR's don't exist any more but the letters seems to have stuck as part of the location code for those places that had just a two letter identifier. eg: ML PH SY DN etc.
Thankfully, when I learn to fly there were no landing charges for GA at any locations in Oz.