Active range is how far a client can move a joint under their own power; passive range is how far it will go when something else moves it for them.
Passive is almost always the larger number, because it is limited only by the joint and the tissue around it. Active is limited by strength as well, so it tells you what the client can actually use.
The gap between the two is the useful measurement. A client whose shoulder reaches 180 degrees of flexion when you lift the arm for them but only 150 when they lift it themselves does not have a mobility problem, they have a strength problem in the last 30 degrees. Stretching that shoulder will not close the gap; loading it through the top of the range will.
Measure both at the start of a block. If passive is also short, then it is a tissue restriction and stretching or loaded lengthening is the right tool.