I checked it with some kl crew members ; and its correct there are restrictions for crew; eg they have to do a test and so on.
Flights on return can have pax from both destinations. Cargo is most important however flights are also pretty full/good load.
CREW Rotations are all shortened . 24h in BKK they have to stay IN THE ROOM../airporthotel. then shuttle and next day back to Ams. No fresh air basically after a 5 day trip...
On a different note KLM operates PVG and HGH via ICN same construction