Some vehicles have turrets configured that can not be accessed. Using moveInTurret has no effect on these turrets, when using 'assignAsTurret' and 'ordergetin' will have an AI unit run to the vehicle, but instead of boarding he will stay outside.
I have tried my best to compile a list with all vehicles and the turrets that are inaccessible. I guess inheritance plays a role here, but to avoid errors I provide my entire list with all vehicle variants, find it in the 'ADDITIONAL INFORMATION' below.