Okay but according to the wiki "boundary=protected_area is used to mark boundaries of protected areas", that's a very broad definition, but "Wiildlife Protection Areas" seem like they should come under this tag.

I don't have any knowledge of IUCN, I simply read the documentation on the wiki for protect_class and found the best match, like any other tag in OSM.

I guess it also comes down to is protect_class meant to be for the officially assigned class, or is it just an OSM tag which can be applied.

In the same way that we set sac_scale on walking tracks here even though nobody is assigning official sac_scale values to tracks.

Sorry but I still don't understand what this has to do with iucn.org.

Yes these may not be in CAPAD but that doesn't mean they aren't protected areas for species protection.