Yes,. Pose libraries are stored as ‘actions’. What Blender does is save the pose on sequential frames of that ‘pose library action’.
First pose = frame 1. 2nd pose = frame 2 etc.
New poses get added to the end and this can be linked/appended to a different file.
You can even use those poses on a different character but just as long as the bones have the same names, anything that Blender can’t match up is ignored.
Hope that helps. Have fun.
