only if you have a stopover?
otherwise im thinking there must be different terms and conditions for different members maybe?
according to my email, SCs can only be earned on eligible flights. nothing about it being counted on a per segment basis (unless I have missed that).
SYD-ADL-SIN on the same day on the QF81 would only earn the total number of SCs based on total distance SYD-SIN which would be 30 for discount Y, doubled to 60. this is the same rule applied for example for a through flight SYD-LHR, you don't get the individual sectors unless you break your journey, or change flight numbers.
in that case, SYD-ADL-SIN taking a domestic flight would net more SCs - 15 for the flight to ADL and then 25x2 for the ADL to SIN sector, for a total of 65.