Originally Posted by
moral_low_ground
...
If I look at JNB-PER via SYD then there is no D showing on either flight.
Yes, appears to be one of those married segment issues.
In my case I also booked what was available although inconveniently timed. I did recheck once every week or so and after about two months D became available on my preferred flights and I was able to change to them.
(It's a shame Experflyer can't do alerts on multi segment routings such as AAA to BBB via CCC. (AAA-xCCC-BBB))