Cr2 file need only one version instance in the file and pz2s need two.  One thing is with a pose file you need a loaded figure to apply it to. I'm curious to how you managed to get the pz2 file to do anything at all. I tried to recreate your findings with your python script modified to open one of my files and found that yes the script works and loads one figure. The pz2 version would not load at all until I had a figure of some kind loaded into the scene and the cr2 version loads perfectly.

Anyhoo... I hope you get it working...