Ah! thanks for that.
The only thing is, I tried other codes as well, for my international Y trips and domestic J trips, for some reason I don't see any promo applied. Chances are, all the searches I did were falling into the category you explained above.
So far, I tried using the codes on the following ;
1. SYD-DEL return in Y - departing 19/Sep and return 28/Sep
2. SYD-MEL return in Y - departing 10/Jul and return 12/Jul
3. LST-DUD return in J - departing any weekend in June for 1 night
Also, if VA releases a DSC sometime soon, I'd be looking to book some more flights, in addition to the above, to make the best use of DSC. And with some fares going up to A$1800 for SYD-DEL return, I'd be more than happy if any of the codes could bring down the fare
I'll keep looking