I know there is also an issue around segments already for me as FB.
AAA-AMS availability
AMS-BBB availability
AAA-AMS-BBB no availability
I have a feeling that this is also an issue for SM.
I see the same availability regardless of route (i.e. C1-C2 or C2-C1), so I have always assumed that the country of your FF# decides POS. My wife's number is based in a different country and she sees different availability than me for a given route/dates.